If he's pulling a 35' TT about 10 times a year, then the engine with 445 hp and 910 ft-lbs of torque is going to get my vote ahead of the 360/380 6.0L GM motor. If he's pulling it once or twice a year, sure. Or if it's always short trips, then gas is fine. But if you're taking trips of any length about once a month, you'll be glad you got the diesel. 910 ft-lbs of torque is no joke compared to the 380 that the gas motor has. Either will certainly handle it, but the diesel is the better tool for the job.
I wouldn't put a 35' TT behind any half ton ten times a year. The GM 6.2L with max trailering package is probably the most well-equipped half ton tow machine out there, but it's still under-sized for a 35' TT ten times a year if the trips are any length at all.
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