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Gears & Gas

This is a discussion on Gears & Gas within the Drivetrain forums, part of the LSx Technical Help Section category; This is my first post on this site! Just so happens, also for the first time, I paid $3.00 plus ...

  1. #1
    Junior Member
    Join Date
    Apr 2006
    Lancaster, CA

    Forest Green
    1998 GMC K3500 Crew Cab

    Gears & Gas

    This is my first post on this site! Just so happens, also for the first time, I paid $3.00 plus a gallon for regular gas. These "firsts" are related.

    I drove my truck back & forth to work this week, as my Jeep is on blocks. That pickup is typically used to haul my slide-in camper, but when empty, it also serves as my backup daily driver. As it works out, the Jeep is so reliable that the truck battery often goes dead from non-use! Anyway, on Thursday, it cost me $75 to fill up the truck, which is a:

    1998 GMC K3500 Crew Cab 4wd 454 cid (7.4 liter) automatic, 4.10 rear differential, with single rear wheels (not a dually).

    All this yields a 10.0 to 10.5 miles/gallon average

    I'd be interested to hear anyones' story based upon their experience of how changing the differential ratio affects fuel mileage. RPM differences are fairly straight-forward to calculate, but I wonder what people actually gained (or lost) in MPG after modifying their differential.

    If the goal is better mileage, do you think modifying the differential is worth the effort?

    Gary P.

  2. #2
    Member ttocs's Avatar
    Join Date
    Jan 2006
    jim thorpe, pa

    98 z28 m6

    A lot of it depends on your driving. Your driving habits will increase your gas milage more then changing your diff around.

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