Double check you have the proper plugs...that are listed on your emission decal under the hood.... That your base timing is correct and your engine is getting up to proper temp, the factory 195f/91c 10190925, is a slow opening unit , I don't remember exactly but it seems full open was over 20f higher, And saw lowered mpg with aftermarket tstats rated at 195f, so we used the correct GM part...also the 5W-30 oil specified in the owners manual. Those are the simple things we saw make a difference back in the day....then there's the differential gear ratio if you have the 3.90:1 that so many 3/4 ton trucks and vans with tow packages had...your mileage is in the ball park ...3.08:1 to 3.23:1 will help mpg on the road....
and if by chance you have a 7.4L 13 is good...
Anil pretty much has it outside of the basic maintenance (tire pressure, plugs, etc) which it seems you've covered. The slower you drive on the freeway, the better your economy. With those aerodynamics and weight, that is going to hold true even down to 25MPH, but of course I'm not advocating you drive on the freeway like that. But keeping it at 60-65 will help. FWIW I get 16MPG freeway with no overdrive and a 5.7L in a full size truck. Forget keeping up with traffic if you want to save gas...stay right, and drive 60-65 using cruise control. Remember that higher speeds require *exponentially* more fuel, it is not a linear relationship (For instance, driving 100MPH instead of 50MPH does not use twice as much gas, it uses much, much more than that, which holds true even for 60 vs 70MPH)
If it's a larger motor than 5.7L, that's decent MPG on the freeway.
the only way your gonna get better mileage on that pig is to hook it up to a tow bar you can check out a 3rd member but you'll want a pro to run the numbers of the ratio for you
"i have a 95 g 20 chevy van".... sell it and get a prius. You have a v-8 powered shoe box. that has the areodynamics of a brick. not alot more to say.
Best idea to get a better mileage, drive a vehicle speed limits.
Some good ideas here:
http://www.gasbuddy.com/gb_tips.aspx
i have a 95 g 20 chevy van and get 13 mpg on the hwy. its well maintained, tires are new and regularly checked for pressure. it has almost 150000 miles but does not burn oil and its changed about every 3-4000 miles. everything is tight and in good repair, no issues with how it handles or drives. just had it tuned and a new air filter put in. it has top of the line a/c delco plugs. what am i doing wrong?
