I've got a '87 300D with 247Kmi. At 77 MPH, the engine usually runs at 2950-3050 RPM, uphill, or flat ground. However, SOMETIMES, it will run 3400 RPM up the same hill that it usually will do at 2950-3050. The only thing I can think - I think it runs faster only when the car is hotter. Is this normal? Seems to have only started doing this more recently, but the weather is hotter than its been.

Also, I've frequently seen the car stay at say a specific RPM, maybe 2200 RPM, and the speed will increase, while the tach stays the same. Is this normal?

Thanks,
Brian