But the way the ECM/PCM uses the temps of IAT or MAT to adjust fueling is differant. Your now an IAT and cold temps going to a MAT ECM so it thinks the engine is cold and adding fuel, when the engine is not cold. It's confused!

The XDF conversion looks correct.

I did see a thread or write up awhile ago on Thirdgen.org about switching MAT to IAT, it's there take a look.