Personally if I were you I'd save up, but a nice truck that can easily handle the load and use that as your daily driver. For 5,500lbs + fuel, water, food, cargo, other people and stuff I'd recommend at least a 1500HD or a 2500.

As far as diesels are concerned you'd be well off with a 2nd gen dodge cummins, or a 94+powerstroke. Both are reliable and both will give you good power and torque and will absolutely manhandle gassers that get in the way, including big blocks. With towing in mind, diesel is the way to go.