Advise on type of truck to tow 6000lb TT
For 6200 pounds, you probably will be best off with a 3/4 ton truck (F-250, 2500, Ram 250). I prefer the 2500HD for a future bigger trailer, but if you don't have any intention of trading up, it might not be worth the extra money.
I have the 6L V8 gas engine in my pickup, and it had trouble pulling my 6200 pound trailer up hills. Diesel is supposed to be better for towing than gas, although with the current premium for diesel fuel, the big block gas engines (like 8L) might deserve another look.
Make sure that whatever truck you get has the heavy duty towing package. The most important component of this is the biggest transmission cooler you can get, so if it does not have this option, you can add it. A transmission temperature guage is invaluable in spotting transmission problems before they cause damage.
I like the long bed extended cab. If you never use the truck except to tow, you can use a short bed (with sliding hitch and/or extended pin box).
The extended cab is great for carrying stuff and people, and more importantly, allows for reclining seats