Know matter how much money you put into your 05 to bring it up to spec the problem is it is still an 05 and the book value would probably be less than what you put into it,IMO consider the 012, Good Luck with your decision.

 

If $ is not a problem then get the new truck. I think you can make your truck work though. If the engine and trans have been reliable, you still have some miles left on the truck. You can put on 17" wheels when towing and keep the 3.92. You can load up some of firewood in trash cans and put them in the trailer if you run with the water tanks almost empty. Oak firewood is about 3500#s for red and about 4200#s for white per cord. Your probably putting in about 1/4 cord in the bed.

I can relate with you on towing with a marginal truck trailer combo. It's no fun at all and scary at times, especially on hilly drives. Good luck.

 

Get the new one! Luck will be you dump all that $ in the 1500 than your tranny will go! Or more. Thr new one will do the job you need no problem plus the warranty!.
Good luck