My fuel mileage just went to junk... 05 lly cc 4x4 sb, was avg 17 per tank and now its down to 13.5-14 hand calculated pretty close to dic #'s, no tuner, daily driven at least 80mi a day for work, 60mi @ 70 down the interstate every day.
Fuel filter has about 4k on it... dic says its down to 28%, running delco fuel filter, run the same brand fuel 99% of the time with no probs checked filter housing for leaks, only mods is an lbz mp, egr blocked and stuck and 4" magnaflow full exhaust no cat. Tranny seems to constantly change shift patterns some times it shifts hard and then it runs the rpm's up with no real accleleration. Any Ideas?

 

Seeing any smoke from the tailpipe or loss of power at any point?

 

No, it's never smoked a lot it's just acting funny. I wiggled all the injector plugs i could reach with out taking any thing apart and it runs like a different truck injector noise is down too.