Mark,
After seeing this, I figured you had bought one and was taking it for a spin already...
Seriously, towing that far with that weight, I'd go diesel (just run it to the store every once in a while when you aren't fishing). I'd look for a 90's powerstroke ford (good years, should be able to find one with not too many miles). Read up on powerstrokes, at some point in the 2000's I think, they started to go to crap. The construction company I worked for before college had to replace something like 70% of the engines of the trucks bought between certain years. I can't remember which years though. I know there was a thread on the "other" board that covered it. I'd stay away from Dodge, but I may be biased.
Good luck,
bob