So the super long and short of this issue is this:

I rebuilt the transmission in my truck and had line pressure issues after rebuilding it. It was basically 60-75#'s and that was it in all gears and it would drop off. Well, after throwing the entire kitchen at it, turns out the Trans-Go boost valve was junk. Stuck a Sonnax LB-2 in it and bingo, trans pressure was right where it should be.

If you want or need for some reason the parts list just let me know, but I don't see how parts are relevant to this issue. I will say, the truck has a
Yank SS3600 converter in it.

So, the tune was in SD at the time. MAF was failed at 0Hz and also in the diagnostics. I had the SES light on. (Not my first time tuning).
So my buddy mentions he thinks something messes with the line pressure that way so just to be sure we left the pressure gauge on it, and I change the exact same tune, to a MAF tune. I turn it back on to fail at 13,500 and adjust the SES light and blow in the tune. As soon as I get out I notice the 1-2 shift is not as crisp, but OK. The pressures are exactly the same. We get it out on the highway, and I have no lock up in the converter, which I had literally, 3 minutes earlier with a SD tune (exact same tune mind you).
I pull over, swap the tune back, and its 100% fine. The tune was never finished, and I would like to finish it and run the MAF, but if I have to choose for now, I will, but it seems like something is going on here and I don't know what.

The ONLY thing I have to look at is I have a Caspers break out wire on it, so it separates the internal air temp sensor from the MAF reading. I have NOT taken this off to make sure its not causing issues, but it wasn't before this whole transmission thing started. Previously, the truck was 100% MAF and running/driving fine before this whole transmission fiasco.

Thanks for any input and help guys, and I know a few guys I hope to hear from!!

 

You need to provide more details about the vehicle and OS. That said, a lot of it comes down to calculated torque in MAF vs SD vs blended applications and what is commanded for line pressure at load/speed.

 

Truck is a 1994 s10. 3440#'s. 6.0/4l65e/3:42's. It has a 02 Tahoe pcm OS : 12216125

From having a line pressure gauge on it, the pressure looked to have stayed exactly the same in SD or MAF. It shifts differently though for sure, so I was stumped on that. I am going to get some scanner data as soon as it stops raining. Here is the tune.

 

Pretty sure there is another code that must be turned off when it's in SD otherwise it jacks with the trans pressure. It's been talked about on efilive.

 

Think about it this way, in SD your OS is using only the VE table for torque calculations and has a finite number of cells to reference (looks like QBert), and will jump rapidly between boundaries. However, using the MAF it is using a nice smooth curve to calculate from.

Again it is all relative to your state of tune in each case.

I haven't logged trans line pressure using SD-only, but in a blended system the commanded line pressure mirrors the MAF signal.