Just took my truck (O2 1500HD 6.0 Liter w/ 3.73 rear end) on a trip and it seems like my truck may be turning more RPM than what I am used to. This is the first trip with this truck, but I had the identical truck before. I am turning about 2900 RPM at 75 MPH. Is this high?

 

Yeah that is. The rear end would at least have to be 4.10's with stock tires. With 3.73's at 75mph you should only be turning about 2300 with stock tires. Check it by jacking up the rear end and using chalk marks.

 

This is probably a long shot, but I had a GMC once that had trouble getting into high gear. Try starting out in low gear at a certain (low) speed, shift up one gear at a time, and note the RPM's in each gear. At least you will know for sure what gear you are in at the 75 MPH/2900 RPM point.

Gerald