I have a 00 silverado with a tci streetfighter converter. I just recently had my pcm reprogrammed, and the transmission now locks up in 3rd and 4th. I like the feel of it locking in 3rd, but I just wanted to know if this hurts anything.

 

nope....not the tranny BUT it could hurt the converter if you are pushing a lot of power and locking it at WOT. I imagine yours unlocks at WOT so you should just enjoy it!!!. I have mine setup to lock up in third as well.