We bought our 2003 new and it has 152,000 miles on it. We have replaced the front ball joints, turbo, water pump, fuel pump, and re-built the trans (47RE). Since our truck is a non HO, 235 HP and 460 lbs. of torque we will replace it with the 6.4 V-8. I suspect that we won't notice much difference towing our 7500 GVW horse trailer.