2002 Chevy 2500 CC short bed 4x2.

So, I've owned this truck since new. Been driving it almost 13 years now and 320,000 miles.

It's been a great truck - other than injector problems. My injectors have pretty much gone out like clock-work at about 80,000 miles each set.

I've always kept careful watch on my fuel mileage, mainly as an indicator that something may be wrong (always injectors in the past).

Last year about this time, my mpg dropped by about 2 mpg across the board. The injectors were smoked (right at about 80k miles) and I changed them out. Thing is, I never got back my 2 mpg like I always have each time they go out and I changed them before. Pretty sure I don't have injector problems that are causing this drop in mpg. Looking for ideas as to what to check??

History on the truck:

As I said, I've owned this truck since new and know the repair and maintenance history intimately. As far as the motor goes, it has VERY little work done to it. I've done most of the work myself.

4 sets of injectors
1 water pump
1 oil cooler to block gasket
Last year, I installed a fuel filter adapter and changed over to the 4 micron Donaldson filters in hopes that my injectors might last longer. Was running stock A/C Delco filters since new.
Truck is completely stock with the exception of the Donaldson filter.

This is basically all that's ever been done to the motor. The entire fuel system, including fuel pump, and everything but injectors, filter and some of the steel injectors lines is factory stock.

Also, one other thing that happens every once in a while might be an indication of a weak fuel pump?? Sometimes, when towing, and therefore burning more fuel than usual, if I turn the truck off for a few minutes, I may have to pump the primer pump on the fuel filter to get it to start back up. Doesn't happen all the time but does sometimes. For instance: Last weekend I pulled my 16'x7' cargo trailer about 700 miles round trip. We stopped multiple (many) times and the trip lasted for 3 days. Only once did I have to re-prime the filter.


The truck still runs great but I'd love to get my 2 mpg back!!

Any ideas / suggestions???