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CM871 Demanded/ 11r22.5 / 13sp

Just wondering what a good cruise RPM is say for 80,000lbs right now at 67MPH in 12th im right at 1600 and i tend to run there as going to 13th drops to around 1400 and it feels like an underpowered fart.


can anyone calculate what my rear end is? when i bought the truck Int said 3.55 on website and Insite in prog-features shows 3.36 so i have no idea.

and no matter which what would be a good gear set to goto for a cruise speed between 65-70 with a buncha rolly polly hills not alot of big ones but alot of updown across i90 in soutb dakota and i80 in iowa

I usually cruise about 1600-1700 rpm with a 2350 and do just fine, regarding calculating rear end, you didn't state your tire size.

Look for a metal tag on your rears. It should tell what ratio you have

theyve been painted by the dealership so any tags on frame/engine/rears would be painted over

I would believe the computer vs the dealer. The ECM has to know the ratio and tire size to calculate the MPH.

well computer had 3.36/512revs which was about 2-3mph off from gps i set to 3.36/500 and its right on.

512 sounds like a lopro 22.5. The 11r is a tall 22.5.

Locate the metal tags like hhow55 said. Scrape the paint off of them. They are aluminum so they won't rust if you're worried about that. The numbers should be stamped so there will be ridges to help you locate them. It sounds like you possibly could have a conflict between what the truck actually has for gear ratio and what the ECM thinks it has.

a bit of gasoline and a paint brush works great for removing the years of buildup.