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Old 09-11-2016, 08:22 PM   #23 (permalink)
Experienced UAW Mechanic
Join Date: Sep 2014
Location: Bear Lake
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The AWD must be costing you a lot more than you think.
I had an '06 GMC Sierra C1500 WT, so 4.3L, 4L60E, 3.23:1, and 245/70R17s. Even with lowering and a tonneau, nothing i tried ever got it over 20 mpg until, i stopped caring about MPG be ause i suddenly needed better towing. I swapped a 4.10:1 axle, got the PCM reflashed, and had no difficulty seeing 22 MPG. For MPG I would have tried a 3.73:1 after that. My similar 94 came with 235/75R15s and a 3.73:1 axle, and was the old TBI, so swirl-port heads rather than the Vortecs, but regularly did 23 MPG stock, and more than once hit 26.
You should actually have less aero drag than my 06, didn't read which engine you have, nor axle ratio, nor tire size, but with a 4.8 and 3.73s you should see 23 if you were 2wd, and you may want to try removing the front shafts until winter. With a 5.3 a 3.42 gear should also do 23.
Doing a cam isnt cheap, the cam alone is 400, plus gaskets, labor, and a tune, at minimum, and you should do valve seals and valvesprings, but would make a dramatic improvement, especially in low RPM torque.
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