2005 GMC Sierra 2500 HD 4WD CNG MPG & Specs — Real-World vs EPA, All Trims

Is the 2005 GMC Sierra 2500 HD 4WD CNG 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 2005 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.

For its most efficient trim, the EPA estimates about $4,950 a year in fuel (15,000 miles) — roughly $412 a month.

2005 GMC Sierra 2500 HD 4WD CNG trims & fuel economy

2005 GMC Sierra 2500 HD 4WD CNG specs

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

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.