Recent content by Helrazzor

  1. Helrazzor

    I've had my obs 1999 GMC C2500 suburban with l29 454 vortec 3.73 gears for 6 years, stock 245/75/16 tires the speedo read to high this is from ecm

    Lift rear tires off the ground, put truck in neutral. Put a mark on drive shaft and rotate wheel one full turn and count the number of times driveshaft completes rotation. That will give you close approximation of what gear you have without opening rear cover.
  2. Helrazzor

    I've had my obs 1999 GMC C2500 suburban with l29 454 vortec 3.73 gears for 6 years, stock 245/75/16 tires the speedo read to high this is from ecm

    Check your RPO codes in the glovebox. GT2=2.29. GT4=3.73. GT5=4.10. GT7=3.33. If it is a different GT code just do search for it.
  3. Helrazzor

    I've had my obs 1999 GMC C2500 suburban with l29 454 vortec 3.73 gears for 6 years, stock 245/75/16 tires the speedo read to high this is from ecm

    3 things will cause your issue. Wrong tire size which you have confirmed are correct. Wrong rear gear, not sure if you have confirmed that. Or the ecm does not have the correct ratio programmed into it. I have a 97 K1500 that is lifted with 35 inch tires. It had factory 3.73 gears that I...
  4. Helrazzor

    I've had my obs 1999 GMC C2500 suburban with l29 454 vortec 3.73 gears for 6 years, stock 245/75/16 tires the speedo read to high this is from ecm

    Stock tire size should be like a 265/75/16. Think you have wrong size tires.
  5. Helrazzor

    Brake Light Issue

    Where is the best place to download the service manual? Scott
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