Industrial diesels seldom - never run over 2000 rpm but that has nothing to do with the engine in your truck. Your truck needs to be running between about 2300 rpm and 3000 rpm to be making peak hp with the Aisin. If you've got your foot to the floor, your in 5th gear and below 2300 rpm you should manually downshift.The 68rfe needs to be in the 2400 - 2950 rpm range to make maximum use of your truck's power. Basically if your foot is to the floor you want to be above 2300 rpm in 5th to make use of your engines power and above 2100 in 4th, otherwise manually downshift.