Won't crank or start - U0100 Code

Well it’s been in the shop this whole time, after having to buy a hard key and waiting for it for the door to by pass the security, now I’m being told by the mechanic that when he hooks up his scanner that it’s saying the car is in 5th gear, said using his scanner tool he can get it in 4th gear but that’s all. Even tho the car rolls in neutral, and won’t in park, the computer is reading 5th gear. Any thoughts?

Unfortunately it’s just a local shop not a gm dealer, and I bought the ecm online and gave them my vin and they programmed it before they sent it out. My next stop is a gm dealer.

I had same problem with GMC Terran 2011 it marked module and I order a new ecm and nothing it was sitting for 6 months intel I started checking wires, there's was this one wire under suv by the alternator black a little thick well that wire is ground goes hooked on to motor block and Then just crank it up. That was the whole thing.