The 3.0 isn't a bad motor at all, despite what many people say. It's not a power house out of the box, but it does have enough torque that it can be used as a truck. They're reliable as hell as long as you take decent care of them. Mine is pushing 200,000 miles, and besides replacing my cam synchronizer (a week ago), a couple of fuel injectors, and regular maintenance (oil changes and spark plugs), it hasn't needed a thing. There were also hundreds of thousands of 3.0's made over it's 20+ year life span, so parts are readily available.
If you're doing lots of towing, offroading, or just want the most power you can get, then I'd hold out for a 4.0. If you want a reliable truck that will get used as a truck from time to time, then the 3.0 will work just fine.