[THEFERMANATOR]

33's and 3.42's with a 4L60E's 30% overdrive is killing your milage. You need a set of 4.10's at leats for that size of tire. Most all stock trucks with 265's(31's) got 3.73's. Most all of the 3.42 trucks got 245's(30's). 12-14 would be good if you drive it conservatively. And just because the engine light isn't on, doesn't mean it is up to snuff. ONLY run AC DELCO platinum's or iridum plugs, good 7 or 8 MM plug wires, the blue marine grade cap and rotor, and the updated MPI conversion set for the injectors is another good investment since the stock poppets were crap even new.