They run much better if you can get the GDE Tune. 8,000 lbs would be near the max for towing. The weak link, imho, is the cooling system when towing. If you tow 8,000 lb trailer up steep hills, want to monitor oil and coolant temps. Other than that, great truck. There is a guy on the Ecodiesel forums with over 500,000 miles on his. Fuel economy is much better if you keep under 70 mph, actually mine does best at 65 mph, over 30 mpgs with the GDE Tune, EGR and DEF deleted. 35,000 miles, I love it.