I was towing my trailer back from vacation and noticed the truck bucking a bit in the top gear from about 1100 to 1800 rpm or about 40-60 mph - doesn't seem to have as much power either. If you pressed on the accelerator gently so as not to downshift, it got a bit worse. If you pushed harder on the accelerator to make it downshift and rev higher it seemed to go away. I pulled into a rest area and stopped and with the truck in park the engine had a vibration at around 1100-1200 rpm but was smooth above and below that. Guess I'm not done pouring money into this truck!! Any ideas..??