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Discussion Starter #1
I've got an 01 2500HD Duramax/Allison with 285/75/16 tires with a 3.73 rear end. What should my rpm be at say 70mph? I don't know if the previous owner recalibrated the speedo after putting on these bigger tires, but it seems like its cruising at a rather high rpm at highway speeds.

Also on the tire it says Max load 1500lbs at 65psi. The fronts are running about 45psi and the rears are at about 55psi. Should I pump them up to 65psi all around or leave them where they are at, or pump them up to the suggested stock 60psi front and 80psi rear? I will not be hauling anything anytime soon btw. And they are Nitto Terra Grappler all terrain M+S tires.
 

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That depends on what your tire wear looks like. If you're not hauling, I wouldn't pump them up anymore than they are right now as you'll have tire wear in the center and none on the outsides. I run 50 all the way around on my BFG's when not hauling, rotated every 6000 miles and I have a pretty even wear.

I can have a look at my tack on the way tonight and post back what I see when I get there.
 

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Discussion Starter #3
They are definitely worn, but I don't drive a lot and they should last at least a couple more years.
 

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Sorry for the delay, according to my Edge Attitude, which is dead on with my GPS, 70mph is about 1970rpm. 70 on the speedometer is about 2070rpm. Hope this helps. With my 285's, 65-66 on the speedo is 70 actual.
 

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Discussion Starter #5
Now is this warmed up because when I first hopped on the highway I was reading about 2000rpm at about 60mph, but when she warmed up a bit it was more like 2000rpm at about 70mph.
 

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SS Duramax;1584534; said:
Now is this warmed up because when I first hopped on the highway I was reading about 2000rpm at about 60mph, but when she warmed up a bit it was more like 2000rpm at about 70mph.
That sounds about right. The allison won't shift into 5th until it has warmed up, approx 100 degrees. It's a built in feature.
 
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