I have a 2004 suburban z71 that my parents bought new. Couple of years ago it stopped going into second gear so I got the transmission rebuilt locally and it came with a 1 year warranty. Soon after, it had the same issue again. Fixed under warranty. 8 months later (less than 1000 miles of (hard) driving) it did the same thing again and lost second gear. It never acted like it was in neutral and free revved, it just wouldn't go into second gear, you'd have to wait until high rpm and light throttle application and it would go into third and then fourth just fine. Out of warranty. I let it sit for 10 months and a week ago I decided to try and fix the issues.

1st thing I noticed was that second gear actually works now, but you still have to wait until high rpm and light throttle. Didn't make sense. I eventually realized it was triggering 4th gear but going into 2nd. Here are my notes from the driving I've done in the last week, only a few miles. :

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2000rpm is 15mph in 1st

3500rpm is 53mph in 2nd


When accelerating from a stop, 1st gear works normally but car does not shift out of first until 6000rpm at zero throttle input. At this point car thinks it is shifting into 4th but it actually shifts into 2nd.



When cruising at 53mph, RPM's are at 3500rpm. This means the transmission is in 2nd gear. Applying throttle makes it try to downshift even though it is already in second gear. Car thinks it is downshifting into 2nd or 3rd and that it is currently in 4th gear.



When accelerating from a stop if the shifter is in "1", "2", or "3" the car will not shift into any gear after first. Once cruising at 55mph in 2nd gear with the shifter in the "D" postition (car thinks it is in 4th), choosing any option besides "D" at that time causes the transmission to act like it is in neutral until the shifter is put back into the "D" position.


Reverse works normally.

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WHEN UNPLUGGING ING0 INTERIOR FUSE PANEL

(


Solenoid a and solenoid b and tcc etc. fault codes present


STILL STARTS IN 1ST GEAR, not third.


)


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This seemed odd, so I whipped up a manual control box to make sure it was the trans and not the truck sending the wrong signal. Sure enough, the following conditions are true: with regards to the shift solenoids:

A on, B on. 1st

A off, B on. 1st

A off, B off. 1st

A on, B off. 2nd

Lockup works fine.

I can hear both solenoids at least attempting to actuate when I hit the switches.

It was overfilled with fluid so I sucked a quart or so out with a pump through the dipstick hole. Drain plug is stuck on. Fluid is dark red and smells new just not as strong.

If it is possibly something I can assess by dropping the pan or changing out a servo from the side I will do it myself. Any advice or insight is all I'm looking for. Thanks.

 

Best guess would be some issue with the second servo apply/release and 3rd gear, With the solenoids a on b off it uses the 4th servo to apply the band in the absence of 3rd you would get second sounds like the servo is somehow venting both the 2nd and 3rd clutch oil.
I would pull and inspect the servo assembly

 

I had similar issues on my 2004 GMC Sierra. Ended up changing the shift solenoids and hasn't been an issue since. It would shift from 1st to 3rd and would only down shift at a stop. I don't think the solenoids cost very much and took me about two hours to drop the pan replace those and filter and refill.