1991 GMC Sierra 2500 4WD MPG & Specs — Real-World vs EPA, All Trims

Is the 1991 GMC Sierra 2500 4WD good on gas?

Real-world MPG vs the EPA number

The EPA figures above come from a standardized dynamometer test, not the open road — real-world MPG typically runs a bit lower depending on your driving, climate and terrain. That's true of every car on this site, old or new.

This 1991 model was originally EPA-tested under the pre-2008 2-cycle method, which didn't account for highway speeds over 60 mph, air-conditioner use, or cold starts. When EPA overhauled the test for model year 2008, city ratings fell by about 12% and highway by about 8% on average industry-wide — and EPA retroactively adjusted every 1984-2007 rating to the stricter standard so old and new cars could be compared fairly. The MPG above is already on that modern scale — the window sticker on this car when it was new likely showed a higher, pre-2008-method number.

At today's AAA national average price — $4.78/gal for diesel gas as of 2026-07-05 — the most efficient trim runs about $3,983/year (roughly $332/month, about $26.56 per 100 miles) at the EPA's assumed 15,000 miles/year, using an estimated 833 gallons a year. We don't estimate a cost-per-fill since exact tank size isn't in the public EPA dataset, but the per-100-mile figure scales to any tank. Current national average gas prices →

1991 GMC Sierra 2500 4WD trims & fuel economy

1991 GMC Sierra 2500 4WD specs

What the EPA test-car listings record for this model year — every combination sold is a row in the trims table above.

Other years of the GMC Sierra 2500 4WD

Similar cars (Standard Pickup Trucks 4WD)

Cars that take premium · Cheapest cars to fuel · Where fuel grade depends on the trim · Fuel guides

1 trim(s) · EPA FuelEconomy.gov data retrieved 2026-07-24 · fuel prices AAA national average as of 2026-07-05.