Hi, I had my 1996 GMC C1500 Sierras transmission rebuilt for the third time, it works OK, but off the line the rpms start to climb and then all the sudden it grabs at about 1400 RPM(1st gear). It seems like its getting to the stall and the TC is grabbing. It feels good from 1-2 and 2-3 and 3-OD. It doesn’t seem like its slipping, there’s no shudder it just grabs at about 1400 RPM. The truck originally had 2-3 band failure. I assumed it may be the TC but no luck; (I replaced the torque converter today with another rebuilt one). I haven’t had a lot of drive time yet, so no codes yet. It actually drives pretty well except for the issue of the line. My rebuilder is pretty unhelpful, he just states I have an electrical problem, but doesn’t know what. I pulled the transmission out and had him rebuild it twice now 1st time was a total failure and the second one was having this issue and an overdrive issue (now fixed). Before my last rebuild it pulled a code p1870, but it was very rare and only happened twice in 3-4 thousand miles.
It has the Transgo shift kit in it as well as a corvette servo. I also replaced all the electronics(except the one on the outside of the trans that attaches to the shift cable) as well as the wiring harness. I also did the computer update from GM (AC12167310).
I just need to work out this 1st gear grab issue. I’m getting really frustrated with this. Does anybody have any ideas????
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