Kay and Gene wrote:
Met a fellow last Saturday towing  a new 35ft outback trailer with a 1500 Silverado.  It was not 4wd and don't know the engine/trans. Said his trailer weighed 7800 and had no problems towing  but said he hadn't been to our nc mountains yet.
 Good point on mountains. I live in San Diego and can't go anywhere but the beach without crossing lengthy 6% or better grades. You can drive these roads (interstate 8, 15 or SR 67) pretty much any weekend and see at least one TT on the side of the highway being towed by a TV that looks too small. I think terrain where you will be towing needs to be considered. 
I have spent a good bit of time in Sequoia and Kings Canyon National Parks. In order to go there with my TT I need to use highway 180. It leaves the valley where the temps are typically above 100 on summer days and CLIMBS AT A 6% GRADE FOR 18 MILES! Believe me, even with an adequate TV you will feel like that climb never ends. If you then decide to drop down to Cedar Grove in Kings Canyon, you'll go through a similar, but windier and more narrow section that's every bit as long and drops almost as much as you've climbed, so you will have the opportunity to test your brakes and tranny. Bigger is better on that road.
On Edit:I just had another memory flash by. Several years ago I was in Southern Colorado. I had my truck camper at the time and was towing a Suzuki Samurai. Somewhere West of Colorado Springs the braking unit on the Suzuki failed while climbing a grade and locked the brakes. It burned the brakes completely out on the Suzuki and I was in the middle of nowhere. In order to get them repaired I had to make it to Durango which meant towing that Suzuki down Wolf Creek Pass with no brakes. Once again the F350 Dually came through, so it's not just the towing capacity that should be discussed in these threads but the ability of the TV to stop the TT in an emergency.