I’ve read many similar posts on here about P0254 and P0088, but after my truck being in a shop for 5 days and $2000 later with no improvements, I’m guessing I may have a brainbuster for some of you.

It’s a deleted, MM3 tuned 2014 2500.

The shop changed out the fuel control solenoid and fuel pressure sensor.

This improved the idle slightly but would not build over 13,100 psi rail pressure.

Plenty of boost pressure, no smoke. (Fuel filters both have less than 1k miles btw).

Today, I put a race plug in the fuel rail to eliminate the possibility of a weak blow off.

Well, now the truck reads 29, xxx psi rail pressure all the time, and runs like a dog.

Sounds like a tired 12 valve.

I did my best to inspect all plugs and wiring, and now I’m shooting in the dark.

Could my return line be obstructed?

Why else would I be building 29k at idle?

Any ideas will help, thanks!