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Pampered-Z · 06-27-2008, 09:52 AM

Also the maintainence and other factors will have a big effect. My DD is a 99 GMC Z71 PU with the 5.3. I get my best highway mileage ( Driving the PA TP over 100 miles each way weekly, if I stay between 55-70MPH ( 70 MPH is 2000 RPMS ), if I exceed 70 my mileage drops noticabley. I assume either convertor unlocks or just the air resistance?

Originally I was getting around 19 highway, I installed a K+N filter and tanoe cover and milage went up to 21-22. When I changes tires to a HD type for towing, the tires weight about 7 pounds move then the previous ones, listed as the same diam., and I use a slightly higher air pressure, and my mileage dropped to 20-21. Since the truck now has 165K on it I've swtich from 5-30 to 10-30 high milage oil and it dropped to 19-20MPG. Next oil change I'm going to go back to 5-30 just to see what effect that has.

06-27-2008, 09:52 AM	#30
Pampered-Z Sliderule / Moderator Join Date: Oct 2004 Location: Catawissa PA Posts: 2,294 iTrader: (1)	Also the maintainence and other factors will have a big effect. My DD is a 99 GMC Z71 PU with the 5.3. I get my best highway mileage ( Driving the PA TP over 100 miles each way weekly, if I stay between 55-70MPH ( 70 MPH is 2000 RPMS ), if I exceed 70 my mileage drops noticabley. I assume either convertor unlocks or just the air resistance? Originally I was getting around 19 highway, I installed a K+N filter and tanoe cover and milage went up to 21-22. When I changes tires to a HD type for towing, the tires weight about 7 pounds move then the previous ones, listed as the same diam., and I use a slightly higher air pressure, and my mileage dropped to 20-21. Since the truck now has 165K on it I've swtich from 5-30 to 10-30 high milage oil and it dropped to 19-20MPG. Next oil change I'm going to go back to 5-30 just to see what effect that has. __________________ 93Z M6 Black: The 385 Lives! Supercharged, 3-core front mount intercooler, GTP heads, 3:73's, Street twin clutch, Jethot Longtubes, Mufflex 4" catback/spintech, S+W cage, Spohn Suspenion, Yada Yada Yada 1) Build it 2) Race it 3) Break it 4) Repeat!!!