2004 GMC Sierra 2500 HD Q&A

2004 GMC Sierra 2500 HD Question: tranny flushed at a shop and since then the shift inhibitor light comes on

and the truck goes into neutral and i have to shut the truck off in order for the truck to go into gear, sometimes in goes into first gear and i have to shut it off again and the engine light goes off -
Answer 1
How many miles on it and ahd the trans EVER been serviced before? Probably sludge contamination -How many miles did the shop test drive it , before returning it to you (if any)? -
Answer 2
What did the shop say is wrong with it now?? -
Comment 1
wrong brand green jelly. -