Engine stumbles when throttle cut-Help

[03 dmax]

I have an 03 Duramax with 140k. Just had an Airdog lift installed and EFI tune flashed. It has a Banks exhaust and wastegate installed prior. Problem is now when you accelerate under load then cut the throttle, the engine stumbles and lopes like it is running out of fuel. This ususally lasts for 3 to 5 seconds, then stabilizes back to a normal idle. The check engine light is on and FPR code comes up. I just replaced the FPR and still doing the same thing.. Please help on what to check next.
Thanks in advance

[WisconsinHick1]

Last time you changed your fuel filter was?

[03 dmax]

Approximatly 4 to 5 k ago at the dealer. Would this affect the fuel at throttle cut after a load.

[WisconsinHick1]

It is possible Im not saying thats it but it could be possible.

[03 dmax]

My Mechanic even put the stock tune back in to see if it would solve the problem. No difference. Now just trying to elliminate all other variables.

Any other ideas???