Hi Everyone, I have a 97' Chevy Silverado ext cab 4.3lt Vortec with 72k Tires: 265/75/r16 max size for truck Stock was 245/70/r16 Exhaust: 1-cat, 1-glass pac and 2-20" tips. Backpressure tested good. The problem that I have had for several years now is poor MPG, 11 city and 14.5 HWY. I was get'n 19/23. Also, the truck lack the "get up and go" it once had. Had the truck to the dealership and put on a TechII twice and all readings are within spec. I will list the thing I have replaced to save time. All parts replaced with OE. New: distrib, cap, rotor, plugs, wires, fuel pressure reg (x2), fuel pump (soon to be x2), fuel filter, tranny, alternator, EGR, pcv, all the O2 sens, therm stat, air and oil filters done per schedule maint. Thats all I can remember. Some stuff listed broke and needed replacement but I listed it any way. Dealership is pointing at my tires and glass pac. Tires I can see for some drop but not that much. Their saying the glass pac is not giving enough back pressure to heat the sensors up so the truck thinks it's running cold and is dumping more fuel. My front hubs are bad and I unpluged the ABS to bypass but that would have no effect. Any feed back you guys can offer to end my nightmare would be great. Thanks for your time!