Re: 2wd or 4wd?
I pull an 8,000-10,000lb center console / trailer combo up our steep local ramps nearly every weekend with an older F350 gasser. It has 4x4, but I've never used it with the boat. My truck is a stick shift and has an open rear differential, with brand new GoodYear silent armor tires.
TONGUE WEIGHT is your friend when it comes to slippery boat ramps, and so is a good set of grippy truck tires. Even with a 1 wheel peel, I barely slip- even with the rears poking into the water. Limited slip differential would definitely be a plus; a true LOCKING differential are not very street friendly unless it is a factory installed auto or electronic locker...I've had both. "Posi-Traction" is simply GM's name for their limited slip's; same as Ford's "Traction-Loc", etc. Aftermarket units definitely work more aggressively. I wouldn't be afraid of a 2wd only truck, but you have to have an idea of what you can and can't do with it. That being said, I'm still a 4wD guy since I need the snow-ability and sometimes go off-road.
I personally like towing with a manual shift truck, but there's some people that should just stick with an automatic. It's definitely easier, I will say that. If you have an underpowered vehicle, or one with too high of gear ratio, or one without a low enough first gear, it requires a lot of clutch work to get a boat moving up a ramp, and someone that goes clutch crazy will get the tires spinning pretty quick, and that can get ya into trouble. Once I let the clutch out a bit, I'm off the brake and on the gas just enough to creep up the ramp at a fast idle with baaaaarely any tire slip.
I think a lot of people may misunderstand the difference between all wheel and 4-wheel drive. "All wheel" drive vehicles have a separate differential unit in the transfer case unit that allow for the differences in input from the front tires when turning. If a vehicle has selectable 4wd, it should never be driven on dry pavement, no matter if it has an open front differential, same gear ratio, or whatever. I noticed someone on here mentioned that they've been driving their Toyota Tacoma like that for years with no trouble; in my opinion, just because someone's been doing something for years and gotten away with it doesn't make it right, it just makes him ignorant...or at least lucky...and that truck will never end up in my driveway!