REDUCED ENGINE POWER!!

I have a 2009 Pontiac G5, i currently haven’t driven it for about 3 months now due to it being stuck in Reduced engine power. I have googled this endlessly and even my Father in law who has grown up working on vehicles his entire life cannot figure this out.
It is throwing the code (P0641 - 5V reference circuit 1. ) I know that there are quite a few possibilities this code could be thrown but I don’t have the money to take it into a dealership or local shop to have a diagnosis.
so if anyone could give advice that would be very helpful!

All present codes are

P0641 - 5V reference circuit 1
P0107 - MAP sensor circuit low voltage
P0452 - Fuel tank pressure sensor circuit low voltage
P0532 - Air conditioning refrigerant pressure sensor circuit low voltage.

now to be fair, I haven’t been able to get my hands on a wiring diagram for the 5V references for the car but since I’ve done extensive research online, I’ve come to realization that all of these codes are probably present due to only one thing on the 5V reference circuit.
I do have a parts car (Same make an model) so there is a chance this will be an inexpensive fix once I figure out the problem.

with all of that being said, can somebody please give me some advice?
I’ve already replaced the MAP sensor and MAF sensor brand new.
Also I’m starting to believe that maybe this isn’t a sensor at all and that it’s a short to ground or a bad connection.
Please help
Thank you