planning on full time RVing... few questions about truck towing capacities??

The tires will be the first limiting factor. And you’ll be maxxed out there. 
Srw will obviously pull and stop it the same as a drw. And with 19.5s if you add them, tire and wheel capacity won’t be an issue. Handling will be better with a dually but with a 5ver, a srw will still be reasonable. 
Biggest consideration imo is what you didn’t mention. How much towing vs how much bobtail driving?  If you’re traveling regularly with the trailer I’d go dually. If you’re moving the camper a couple/few times a year and staying put and the truck is a daily driver more than a tow rig, I’d go srw. 

It's all about payload. Almost always, people run out of payload before they run out of tow rating.

In that size range, you are looking at a pin weight around 3500-4500lb (20-25% is typical). Pin weight counts against the trucks payload. Also, the weight of people and gear in the truck along with bolt on aftermarket items like running boards. You could easily be north of 5000lb in the truck.

 - SRW trucks top out around 4500lb payload but that will generally be the gas regular cab. If you get the extended cab diesel (and in that size range, I would want diesel), it will be lower. I won't say it's impossible but very tough to stay within the weight ratings.

 - DRW trucks start around 6500lb and go as high as 8000lb payload. That gives you plenty of room on payload.

I will almost guarentee you will need a dual rear wheel for that weight of rv.  not only does it give you more stability on the road, but you are looking at a pin weight around 4000lbs or more.