A freind of mine has a 95 12 valve 1 ton dually no after market parts accept for a flat bed and going down the highway he can only get to 65mph and thats at 2500rpm

 

I would suspect the following things, he may still has the OEM single piece overflow valve (if so, he is lucky to be running at all), if he may be running up against the defueling curve of the injection pump because of slow timing, or his fuel filters are plugged (the most common problem with filters in that era is the screen in the fuel heater gets rusted shut). It could be old fuel hoses allowing air infiltration, a lift pump no longer outputting the needed volume of fuel, air leaking in the electric plug of the fuel heater, or even the pickup hose in the fuel tank starting to fail (that is pretty common for those trucks, too). Anyway, there are a lot of things to check.

 

Sounds like he needs a 3k GSK, it is defueling a bit early. He must have a 5spd tranny. Using a speed/rpm calculator, he is running 65 @ 2200RPMs, with 4.10 gears. The gearing itself and the small (215-85-16) tires aren't helping any, speed-wise.

Other than taller tires, GSK and a possible plate change , that's all she wrote. The #10 plate has allowed me to turn slightly higher RPMs. I have 4.10 gears, also.

 

Thanks ill tell him that.