Hello all. Anthony here from Yuma, AZ. I found this site trying to troubleshoot a new to me 1991 Suburban 2500 with shifting issues. It comes and goes with cycling the ignition and causes it to not shift until way to high speed/rpm. I ordered my ALDL to usb, downloaded TunerPro RT and went on the hunt for the appropriate xdf/adx files. I have a lot of experience in older carbureted cars and worked for VW 20ish years ago so had experience with the VAGCOM. My scan tool does obdd2 live data, but not obd1 so this is new to me using TunerPro RT. I'm loving it so far. I can see that issue happens when the PCM gives up trying to get info from the drac and choses the transmission output sensor. For whatever reason, when it does that the PCM thinks the speed is about 1/2 of actual and thinks the transmission is slipping so it also maxes out the line pressure causing high rpm and hard shifts. The speedo always works and displays the correct speed, so it must be something wrong with the signal from the drac to PCM. Checked and cleaned all of the grounds, and now I just received a handheld oscilloscope so I can try to see what the signal looks like. I used the $85 xfd and A150/A138 ADS converted to ADX files, but looking forward to some of the newer files done by EagleMark. I'm a programmer, but C#/.Net stuff, so I haven't quite got my head around how the xfd/adx file where created, so thanks for the work and sharing it with us all!