Yes you can consider a gas powered Excursion, however the heavier diesel version is to heavy to have much towing capacity.
Any of the big 3 V8's will provide plenty of power. They all make over 300 HP, and that is so much more than the 'Big Blocks' of the 70's and 80'. Ford's 5.4L that I had in a E-250 work van was great, got 11 MPG in city driving, while about 8,000 pounds curb weight on Chevron gas, but only 10 MPG on Arco or other brands.
The Dodge 5.9L gas is also fine. GM 6.0L is what my cousin had in a dually cargo van, and it also had plenty of power in the mountains around Colorado.
I would avoid the V10 unless you really must get there very quickly, and do not mind paying the price at the pump.
The Ford Excursion is also a good SUV for towing, it has a 8,000 pound +/- rating. It came with the 5.4L V8 until recently, when the Ecoboost 3.5L is offered, and many are trading up for better mileage, and more HP.
If you are only going to put 5,000 miles a year on the vehicle, then why worry to much about gas MPG? You will be buying less than 1,000 gallons a year anyway. I would stay away from a diesel, due to it's much more expensive oil changes, and other maintenance.
Good luck,
Fred.