6nz cat loss of fuel mileage.

Hey guys I need some help here please. I got a 2003 379 pete with a 02 6nz C-15 with a PDI stage one tune, turbo and manifold. Power is great no loss, fuel pressure great, new CAC, radiator and AC condenser. I checked all fuel lines they are clean n flowing properly, no leaks no raw fuel smell out the straight 8" stacks no colored smoke, no codes thrown. Did have #6 injector fail 2wks ago and cat replaced found by the dyno put a reman in. NOW here's the deal, slight miss at idle but not while going throughout the rpm while loaded. Fuel mileage dropped from 5.6-6.0 to 4.5-4.8 regardless of a 45,000 or a 20,000 lb load. As I said NO POWER LOSS just fuel mileage dropped. Thanks

 

the other 5 injectors are original new ones probably 10yrs old. The cac is a duralite the one PDI sells. I wanted to put all new 6 in but cat was out n had to order which I didn't wanna be down for 2days so the reman went in 10r8501. But in 950,000 miles never had an injector problem till then. Oh and all trim #'s are set as per each injectors I don't believe in the other power trim #'s

 

I really appreciate y'all's info here I know you guys probably have answered questions like this over a thousand times but I'm just learning this cat engine knowledge as I go lol

 

okay guys I found the problem the timing gear was off one tooth which caused the back lash adjustment to be off and it was throwing the truck almost outta of time where it wouldn't of run at all and got it fixed and now I'm back up to 5.6 to 6.0mpg