and that is the problem, if your pulling up a good grade, my GMC 1500 5.3 V8 is down to second gear and 4000 rpm at what seems to be 35 MPH with a 7600 pound trailer. It makes you gun shy of gas trucks when the local Pepsi distributor truck passes you like your sitting still while haulin a full load of Pespi's while your sitting on 4000 RPM's going up good hill in the Smokey Mtns. In camping at variousRV parks you find there are an awful lot of Ram, Ford, and GM diesels 2500's pulling 13-15,000 pound 5th wheels.
