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I got a gen IV 5.3 with a plethora of mods in a trade. The engine has a stroker kit, 4l80 swap, two piece driveshaft, and Yukon rear end. The thing I'm having problems with is the trans. I was told it has a billet adapter plate, high steel convertor, and maybe an upgraded valve body. First problem, there's no indicator line under park or neutral 3rd or 1st. Second problem, if you put it in drive, it seems like it's in 3rd gear. I drop it down to manual 1st and it seems to go in 2nd. It'll drive kind of normally after getting moving. 3rd problem is the reverse feels like it engages but it barely moves if you're on flat ground.
I can do engine rebuild and swaps but never got into diagnosing transmission problems.
Edit: the wiring harness on the NSS has 2 grey 2 white an orange and a yellow wire. All the diagrams I see have 12 wires.
Update: I adjusted the NSS for a while yesterday, nothing worked. I took it off and left it off all night, today I put it back on and it works perfectly. No idea what I did but I can program my TPMS now
Are you saying that you now have Reverse working too? And it starts in 1st gear?
I don't see how the NSS (Neutral Safety Switch) can have anything to do with that. Perhaps the main trans connector is flakey and you bumped it while working the the NSS. (Although even a disconnected trans connector will give you Reverse).
Newer Vehicles will have multiple Types of Body Control Modules, as well as the PCM, IPC and VCM that will cant to communicate with the NSS Position/ Data...
Class-II Data or GM LAN both work this way depending on the Vehicle.
Previous owner built it for drag racing, it's got a 3800 stall converter. He threw in the towel after the trans was rebuilt and the gears starting going.
The NSS problem was that the gear indicator was only lighting up every other gear, as a result the locks didn't unlock in park and I couldn't reset TPMS. The transmission knew what gear it was in but maybe wasn't relaying it to the TCM/ECU whichever it is.
It's got 6 wires coming out of the wider 12 pin harness.
Reverse feel like it engages but barely moves the truck on flat ground. Drive starts out the same way, it's barely moving forward. Doesn't really feel like it's slipping, but idk. If you put it in 3-2-1 it starts in what feels like second. Once you're on the highway drive engages.
You should have the newer Single Connector Style NSS.
Post an Image so we can see which Wires/ Circuits are missing, and if that could be related.
If things actually work well enough with the NSS the way you have it (Unlikely though)...
Are all Control Modules active within this Vehicle?
The loss of Communication with the Tire Pressure Monitoring Control Module (TPMCM) is odd...
Then you may have a Data-Line/ Data-Buss (Class-II Data) communication is with one or multiple modules.
You would need to start out with a Scan Program or Tool that can look at the other 30 Module in the Vehicle other than the PCM or TCM.
Look for "U_ _ _ _" Codes and also "B_ _ _ _" Codes.
Also look at live Data for missing Sensor Data to try and run down a Sensor/ Connection issue.
Last edited by vorteciroc; Jul 1, 2023 at 04:08 PM.
I fixed the PRND indicator light by playing with the NSS and walking away a few times. No idea what I did differently the 3rd time but it works great now. I programmed a key fob to celebrate. So now it just feels like a weird transmission. I've never had a high stall converter before so revving higher to move from a stop is different. It overall feels like a manual transmission and I'm a teenage driver learning to use the clutch. If I put it in drive it may creep an inch but revs like it's slipping like the clutches are partially engaged. Reverse is still the same it'll sort of move, mostly free revving. So I put it in 3 at stop lights to get it into gear then it revs up to 2k before it moves which I assume is the high stall. Then it shifts at 20mph and 33mph. If I put it in drive it acts like it's in neutral. Once I hit 45mph it'll shift into drive then at 55mph it shifts into overdrive. It downshifts weird. It'll stick in overdrive till 40mphs or I rev it, then it'll miss the gear unless I take my foot off the gas to let the gear catch. Reverse will sort of move me on a flat surface but I usually put one foot out to help push it backward. The brake and abs light pop on after 10-15min of driving. I need to get access to a tech2 scanner. There's a wheel speed sensor code.
one thing unrelated that may be related is the estimated mpg is absurdly high. I think the trip is off too. Makes me think something is off in the tune.
Is there anyway to change the idle permanently without forking out a few hundred for HP tuners?
Also why do I need credits to tune my truck, why can't I just use the tech2 scanner. I
I fixed the PRND indicator light by playing with the NSS and walking away a few times. No idea what I did differently the 3rd time but it works great now. I programmed a key fob to celebrate. So now it just feels like a weird transmission. I've never had a high stall converter before so revving higher to move from a stop is different. It overall feels like a manual transmission and I'm a teenage driver learning to use the clutch. If I put it in drive it may creep an inch but revs like it's slipping like the clutches are partially engaged. Reverse is still the same it'll sort of move, mostly free revving. So I put it in 3 at stop lights to get it into gear then it revs up to 2k before it moves which I assume is the high stall. Then it shifts at 20mph and 33mph. If I put it in drive it acts like it's in neutral. Once I hit 45mph it'll shift into drive then at 55mph it shifts into overdrive. It downshifts weird. It'll stick in overdrive till 40mphs or I rev it, then it'll miss the gear unless I take my foot off the gas to let the gear catch. Reverse will sort of move me on a flat surface but I usually put one foot out to help push it backward. The brake and abs light pop on after 10-15min of driving. I need to get access to a tech2 scanner. There's a wheel speed sensor code.
one thing unrelated that may be related is the estimated mpg is absurdly high. I think the trip is off too. Makes me think something is off in the tune.
Is there anyway to change the idle permanently without forking out a few hundred for HP tuners?
Also why do I need credits to tune my truck, why can't I just use the tech2 scanner. I
These Jerry-Rigged Builds drive me crazy...
There is NO WAY to know if something might work or not!
Diagnosis is a JOKE!
I know people will always cut corners, and in some instances it is practical.
But in these situations, please, please just Wire everything properly.
The GM Tech-II was created to Monitor, Control on a Temporary basis for Testing and up until 2010, Perform Complete Software Updates.
It NEVER was able to permanently alter single parameters.
That would violate State and National Emissions Laws.
It's rigged for sure but surprisingly clean.
I just talked to a shop that worked on it a few years ago for the previous owner. He said replace/rebuild the trans. What he said was that with 4l80 if it doesn't have reverse than it's got to be internal and not a computer problem. The reverse is purely hydrologic I guess. I forgot to mention that the trans has a valve body rebuild kit in it. I found the instructions for it behind the seat. All in all if I can get the trans to shift, some AC, and mufflers, I'd be set.
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No park neutral indicator on dash 
