Looking for truck

Guys,

I'm in the market for a diesel pickup truck to haul a 12K lbs three horse trailer. I don't expect to ever go over 12K lbs.

I'm pulling a 5K lbs two horse bumper pull with a 2002 F-150 5.4L truck now. Its pulling fine and the truck only has 128,000 miles but I want to haul the heavier trailer that my F150 cannot handle.

Looking at a F250 or F350 diesel and I'd rather save some money and buy used. I'm open to a Ram also but more familiar with Ford.

My question is diesel the right way to go or is the 6.2L good enough with the weight I will be towing? This vehicle will only be used for towing.

What rear end? I have a 3.55 Limited slip in my F150 now and the limited slip has saved me in the past.

My last question is am I buying a couple months to early? With the 2017 Aluminum bodies coming out do you think the 2015/2016 used truck values/prices drop in September/October?

Never owned a diesel before and I do all my own maintenance. I have a 6.8 V10 E350 RV and love the engine.