2000 GMC Jimmy SLT getting really bad gas mileage

[Tupac2413]

When i first bought it it drove good and had good gas mileage now it gets about 15 miles per gallon on the highway on cruise control and even worst not on cruise control i bought some slightly bigger tires on it like 6 months ago would that have the much of an effect on the gas mileage?

[velocity1]

I had the same thing happen to me with my 2000 Jimmy. I just did a full tune up and noticed a big difference. I used the Bosch +2 plugs. K&N Intake tube and filter. I have 85k on it.

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My wife had just bought her 2000 jummy last year and is getting around 15 also, what type of milage should she be getting?

[jqcas]

well i don't know but these little trucks get pretty bad gas mileage, my mom just bought one (worst mistake ever), and it hardly gets 15mpg...

[luscombe8]

I have found the following problems with mine and they changed the mileage dramatically.
1. Front left hub was going bad, there was a hum that made me inspect it.
2. I tried bigger tires, they had a more aggressive tread pattern for snow country, but when I changed back to road tires, the mileage improved again.
3. The car had 132,000 miles with the original plugs, when I installed AC Deco double platinum the mileage went up,
4. Both the front and rear right brakes were dragging. I had replaced the rotors with aftermarket stuff and the thinner thickness of the rotor blade made the pistons travel out further and they would drag. Going back to original stuff eliminated the problem. What a difference running the car with the brakes off made.
5. I swithched to Mobil 1, I guess any syn oil will do, but that helped too.
6. I backed off of my 75 mph cruise speed to 60-65 and it helped too.
7. I had a 4 wheel alignment by a good shop, not the fronts, but all 4.
The car now gets 21mpg on the highyway.

I hope this helps.

[maxwedge]

Great advice, but please look at the dates before posting this is waaaay tooo old, thanks.