ihave a 2001 2500hd that will run for a short time then power down. when this happens if i hold the throttle steady it will lose about 5 to 6 mph and continue running just fine, if i give it more throttle then it will power on down to where it will only rev to 1900rpm or 25mph, and continue to run just fine (not missing) just will not rev more than that. if i shut the truck down for 5 to 10 min then restart it will run just fine for 2 to 5 min then repeat it all over again. any ideas thanks