2015 Camaro LS3 Key will not program to car.

Hello! I just want to start by saying I'm just dipping my feet into the LS Tuning world. I will give some background on where this all started and how it has gotten to this point. I purchased a 2015 Camaro 1LE stolen recovery car the end of 2018. The car had the Motor and transmission stolen from it along with ecm. Everything else was there. I've fixed up all of the body work needed to be done and was ready to do a motor swap into it. Looked around on Ebay and found the motor, It was a 2013 Camaro SS 1LE aswell with a few modifications done to it (Cam, rockers, pushrods, pully, headers). Got the motor home and into the car smoothly and everything plugged up. This is where it gets interesting. I plugged the ECM from the Donor engines car into my 2015 Camaro so I could plug HP tuners into it to possibly change the VIN and maybe make my life super easy. That was not the case. I could not change the VIN and ended up ordering an ECM from LSSolutions with my VIN and Sent him the Tune from the ECM that came with the motor to put on it since it was previously tuned. Thinking once I had gotten the ECM I should be able to plug it in and take my new GM Key and do the 10 minute 10 minute 10 minute key program and turn the engine over. On the very last step right before the Security light was about to turn off the Theft deterrent light came on and flashed and posted on the screen service theft Deterrent system. I get the code P0513 "Incorrect immobilizer key". I've talked to GM and they really don't know and want to throw tons of R & R and time at it. I didn't know if it could have something to do with it being a used ECM or even throwing the previous ECMs Tune onto my VINs ecm is having anything to do with it not letting me pair the keys to allow me to turn the engine over. I will say I have had another ECM put into the car for a ZL1 engine we were going to go with previously and the paired perfect with the key doing the 30 min cycle and now this one is just a headache. Do you think throwing the stock tune onto the ECM would help getting the key to pair then throwing the tune on? And if anyone has a 2014-2015 Camaro SS 1LE stock tune that would really help! Any advice or tips would be SUPER appreciated. Thanks!