We have a 2013 ECO 4x4 crew cab short bed 3.55. 48,000 miles, 12,000 plus towing.
We tow a similar TT. Ours is 4900 empty / about 6100 loaded. We have a WD hitch and it tows great. Replaced the tires in Dec with Michelin LT tires and added Bilsten shocks. We have no problems with the short wheelbase being a stable ride. It actually towed great before the new tires and shocks too.
We tow to the Keys at least once each winter, about 2000 miles for the trip. Overall mileage towing is 10.5 mpg avg. Will vary depending a lot of wind. Range is from 8.5 to 12.5 but on a long trip avg always seems about 10.5. Just made our first trip to NC mountains and averaged about the same 10.5 on a 1000 mile trip. We tow around 62-65 miles per hour. Faster or slower will definitely affect your mileage. Mileage not towing with a mix of driving is around 18.5. Can go up to 20-21 if on a long trip and you are not doing 80 :).
The truck has great power and I would not worry taking it cross country. We are actually thinking about doing that. From NC coast to the Keys we set cruise and it rarely will drop out of 6th gear. In the hills I locked out 6th and dropped cruise in the real hilly areas but it still performed great.
Long term reliability is to be determined. Some folks question that on the ECO. I don't think it is an issue. Only thing we have had to repair was a battery gone bad under warranty and a couple of minor recalls.
Ours is not a max tow or max payload. Don't see it necessary with our size TT.