I have been weighing the idea of getting a camper to haul on long road trips but I would like some advice on what size to go with. I would like to mix comfort/leisure (sleeping 4, while equipped with a toilet and shower) while minimizing weight on the truck and maximizing engine/truck efficiency. I would prefer to go with a 5th wheel style because I have found they tend to feel less heavy on the truck while driving, and put less stress on the vehicle overall. The least preferred would be a pop-up camper, due to the lack of a washroom (toilet and shower).

I guess my question really is, what do y'all pull with this kind of truck and what kind of stats (temps, best cruising speed, mpg, etc..) do y'all see? My experience is mostly with diesels and this is my first gas engine truck. If it happened to have a 24V Cummins, or a Detroit(GM) 6.5L TD, I would know exactly what it can handle. With that being said, I'm a little behind the knowledge curve here.

Michael the good news is many manufacturer'* are making lighter & larger travel trailers today. IDK if you want to buy new, but warranty regardless is important.
The other good news is that there are always many used trailers available in the marketplace.
Size, well that truly is a personal choice based on creature comfort & conveniences etc.
What I would recommend is going firstly to an RV center and have the family look around at interior layouts, features, pop out etc and find the smallest trailer that fits your needs.
Review online trailer qualities, and look for more robustly built trailers if long hauling.
Most importantly electrical, new tires, bearings, and having new spare/* if buying used.
5th wheel is the best way to go for trailers over 24' smaller trailers under 7000 can be towed with correct truck hitch & trailer brakes no problem.
The obvious advantages to diesel are torque, pulling weights & mpg.
Hope you can find a trailer that the 4 of you feel comfortable in.

I agree with Soft Ride. Also I don't see whether your truck is a 1500 or 2500 or 3500. The 6.0 could be had in all. If 1500 then I'd suggest keeping the weight down, and perhaps think about adding a transmission cooler to whatever it already has.

If larger than 1500 then less of this to worry about as the axles, suspension, and transmission all are a lot more serious.

If larger than 1500 perhaps you might want to look into a slide-in cabover camper? A bit more weight actually on the truck but often easier to deal with, and about the same frontal area as a trailer. Like Soft Ride says, they're making a lot of the new ones lighter . . . but I wouldn't put one on the back of a 1500 no matter what the brochure says.

Well, of all of the things I put in my signature, the weight rating was the thing I forgot. Brilliant. (It'* updated by the way).

I have a GMC Sierrs 2500 (not the HD version).

I believe I would like to steer clear of the in-bed cab-overs for a couple reasons (one of which it would have to house 2 adults and a baby).

This leads me to another question. Does the 2500 series come stock with a transmission cooler? I've noticed here in the Carolinas where it gets to 90F+ in the afternoons, and I've been in normal city traffic (45+ MPH w/ stop lights), my transmission temperature hovers just shy of 200F (in the 9 miles I commute), but never exceeds 200F (even when getting on and off the Insterstate at HWY speeds).

Another question that shows my ignorance (because this is also my first automatic, as well as gas truck), what all exactly does the "Tow/Haul" mode actually do (besides change the shift setpoints, and make each shift a little tighter)?

Thanks!

I believe they all (2500/3500) do come with a transmission cooler of some sort.
Same truck as a landscaping truck probably wouldn't eat a transmission for 150,000+ under hard use with no add-on.

That having been said, from my past I've never seen a transmission run too cool after warm-up. My fleet includes three TH400'*, three 4L60E'*, two THM250C'*, a 4T60E, and a 6T70 with varying levels of external coolers on more than six of them. Maybe if you were driving empty through northern Alaska in winter or somesuch then you could see an issue . . . ? I haven't tried it. 20 below in CO never seems to be an issue. If you have the opportunity to install an add-on transmission cooler then I'd suggest it. I always put mine in-line after the factory cooler.

Tow/haul does what you say, thereby preserving the driveline a little longer than otherwise. It also removes some unnecessary hunting, especially between third and overdrive (on yours) and allows you better fuel economy in non-tow/haul mode than a one-size-fits-all shift map.