The plugs were replaced at 50k miles just turned 60k. I run royal purple motor oil changed every 6k miles or once a year. The transmission I drop pan and replace filter every 15k. The truck is very well maintained and hasn't really ever towed much. The tires are a all terrain not very aggressive tread. The trailer is 3300 lbs empty. I have a 1200 lb mid size utv in the bed and added 1000lbs for clothes, camping gear and my wife and I so that is where I get 5500 lbs. I have air bags so the truck rides nice and level with the load. Yes About 4500rpms you feel the power problem is locking it in second with foot to the floor it keeps loosing speed till it shifts down to 1 st gear picks up speed and about 6000 rpms shifts back to second eventually looses speed and same all over again. I know the Hemi likes rpm's so I let it run, but it won't hold 2 nd at 50 mph and 4800 rpm just keeps loosing steam the longer the hill is. It does seem like a combination of poor gearing and power.
