hello

I have a 2006 express 2500 v8 4.8l. with 120k miles. trans started acting up late last year. there was a code to I think it was trans related. lost of power and kicks when shifting after long drives.
took it to a local guy who as done some trans rebuild for a cpl people who are happy with the work. so he rebuilds it. I drove it seems ok. however when its on reverse the engine dies, I have to restart and push gas to keep it from dying on reverse. Drive seems ok and shifting is ok. took it back and he was trying to fix it for a week. even put in another tras unit. still doing the same. drives ok but after it warms up the reverse shuts the engine off. no codes. he even changes the throttle body. I am using it since I need to work however it needs To go back. any ideas what the cause ? hes willing to do what it takes to make it right. he is saying its an electrical problem? it did not do that before however. im the original owner. dealer did a flywheel repair many years ago under warranty. that's about it. no other work was done to the trans.

any help with be greats

thanks

Zach