Not my car, but trying to help a buddy out. He's 3 hrs away from me as well Lol.. anyways, he's about ready to part it out and sell it after throwing $1100 worth of sensors n **** to try n fix this issue to no avail so far. Has new PCM, new fuel rail pressure sensor, new maps, new maf, and new battery that I know of. Yet it still shows up as map sensors low voltage.
Car has 3bar sensors already...

Any ideas besides new wiring harness? Lol

 

Assuming the tune on the new ecu is correct for the 3bar?

I'd pull the loom apart and chase the wires back or find out what voltage is supposed to be at and verify with a multi meter. If you can find a pinout diagram you might be able to test the resistance between map wire plugs and the ecu harness.