When you find yourself at the top end of the "1/2 ton" capabilities there is a trade-off. Milage and comfort for daily driving vs. heavier capability. For your existing trailer or limiting the trailer at 7k or so getting an F150 with the 3.5 EcoBoost and max tow package would give you improved payload and wheel base providing greater stability. The 3.5 EcoBoost makes a lot of torque down low and makes for a more pleasant drive (less downshifting for hills).
I tow 8k, but I have the max payload option that you pretty much have to special order. I knew I would never get a larger trailer and I also preferred the F150 over the HDs for a couple reasons. Although this was the right solution for me I do not recommend this because if you go this route you are maxed out, there is no room to go heavier.
VernDiesel drives the Ram 1500 EcoDiesel and has given many positive reports. He is an experienced driver and has towed up to 8k. One of these with the air suspension should be comfortable as a daily driver with about the best milage you will find in a "1/2 ton".
ib516's recommendation for the Ram 2500 with the 6.4 and new 8 speed transmission (and 3.73 rear end) is a good one. My neighbor has the Ram 2500 and the coil springs offer a good ride. There were some complaints with the with prior years about the spacing in the gearing but with the new 8 speed that should be taken care of. Also, the heavier truck will do better if you deal with side winds or long downhill stretches that would benefit from some engine braking.
So, long story short, if it were me I would test drive (and read payload stickers) on the F150 Max Tow, Ram 1500 EcoDiesel, and Ram 2500 with 6.4 and see which one you liked best. Scout out a test drive route in advance with some bumpy roads, and some freeway, etc to get a feel for it. Also, make sure the truck comes with LT tires. If you want an idea on real world mpg on these or other rigs check-out fuelly.com.
Take it easy,
Stu
p.s. The payload on the Ram 2500 is understated so it fits in a particular registration class. It is a lot of truck.
p.p.s. I see you are in OK. Tulsa? If yes the cinnamon roles at the Savoy are really good. Will be there in a couple of weeks and we always stop in to get one.
