Good question Derek, Rob disconnect the return line from the FPR and blow through it, any resistance? If that line is blocked pressure will go too high and could cause the FPR to leak.

Also some other questions.

Have you done a compression test? Poor compression can lead to overfueling.

Have you tested the coolant temperature sensor with an ohm meter?

Check and clean the grounds where a number of FI wires attach to the intake manifold.

Very high idle is false air , you mentioned previously that the injector seals you received with the new injectors from VP were “no good “. What do you mean by no good? AFAIK the injectors sold by VP are the Beck Arnley ones , I use those too. Unlikely they are bad when new.

Is the gas tank clean and gas reasonably fresh? Sediment in the gas could cause an injector to malfunction.

Try snugging up the intake manifold nuts where it attaches to the head, not overly tight, just to make sure they’re not loose.

Have you done a vacuum test on the MPS?

Please check these one at a time and report back.