So here's the deal. Our trusty Myrtle started guzzling engine oil so in July I got my hands on a really nice looking crew cab with 71000 miles. The truck has a banks trans command and a kenne bell supercharger. It also had the dreaded exhaust leak. We drove her around as is and it was fine except for the smell of exhaust on start up and the noise. I finally was able to bring her in to get that leak fixed by having the local muffler shop install some Thorley headers. They also took the cat out and put in a new muffler. I should have gobs of power right? I can't tell the difference. At least it sounds nice.
I also noticed that my mpg took a huge dump, we're about 500 miles into a 6000 mile road trip right now and I'm getting around 8 with our 2000 lb Alaskan camper and pulling a 1000 lb teardrop trailer. Going 45-65 mph, not many crazy grades. Front tank only, I'm in the process of checking the rear. Before I brought it in it seemed to be closer to 10-11 mpg. The mechanic did do something to the fuel system: he said he noticed that there was an open vent on the front tank which he plugged. The tank is aftermarket. Thanks for reading

 

Did the shop re-install the O2 sensor in one of the header collectors?

 

I don't know. I shall check, right now.

 

Yup it's there

 

One item down....many more to go.


Age/condition of the plugs, wires, cap/rotor?

Air filter?

Tire pressures?

Check for dragging brakes?

Check for fuel tank cross-flow.

Fuel pressure running on the front versus rear tank?

Have you checked the Fuel Pressure Regulator for signs of leaking?

Honestly 8-9 MPG on a 460 equipped truck carrying a camper is not that bad IMHO...

 

Considering mine only got 10 MPG around town unloaded, with a great running and properly tuned 460, I'd say you should be thankful for 8-9 MPG!

 

Just Like they said, 8 to 9 seems normal to me. Ecspecially when carrying around an extra 3,000 pounds.