The V6 will be way over its tow ratings with an 8000 lb load. If you have at least 500 miles on your 2003, I'd use it. We first pulled our 13,500 lb 5ver with about 530 miles on the current truck. Frankly, at that mileage, it didn't pull nearly as well as our 3500 V-10 that was still sitting at the house! It got much better at 1000 miles and again at 2000 miles (I'm convinced there's some break-in programming in either the ECM or PCM), but even at 530 miles, it didn't overheat or use any oil.
The recommended break-in period before towing is (IMHO) there to allow seating of the rear axle ring and pinion wear surfaces more than the Cummins.
Rusty