ok guys heres my problem I have a boosted 2002 Silverado that I just did a 4l80 swap on . I changed harness and loaded a tune from a 02 2500 . the tranny locks ups the tcc in reverse every time ,any ideas what it might be .the tranny is 2004 model . thanks for looking

 

Internal problem. Try increasing the idle speed. You can also change the PR valve to a Sonnax line to lube and see if that helps.

 

I was having the same issue, i picked up a take out trans to replace the other unit that was causing the issue and it seems that the issue was an internal leak of some sort. I thought it was an electronic gremlin since I was swapping a 4L80e into my GTO but it was the trans itself. Its probably a cross leak.