Say mostly stuff not too heavy but 6000lbs like a car on a 16 or 18ft 2000lb trailer? no good or great with their HP/torque numbers?

 

they pull great but are rated for 5,000lbs tow rating. you'll be exceeding the class III hitch rating after that, so at a minimum it would need to be replaced. not to mention many other factors go into that rating. folks have pulled more than that but not so sure what their setup is. 99s had a little softer suspension and less payload capacity (like 800 lbs) and then in 03 it was stiffened a little bit and capacity raised to I think 1350. provided your hitch is appropriate, trailer loaded properly, not too much/little tongue weight, and appropriate brake controller... 6k is probably safe. get an EGT gauge to monitor exhaust temps if you'll be pulling any hills/mountains. and stay at stock boost levels or no more than 2lbs additional with a fuel heavy tow tune. my 2 cents