If you go the Grand Cherokee route I'd say, for proven longevity's sake, stick with the I6. The V8s are nice, but your towing capacity is limited more by the chassis than available torque in this case, so there's little to gain from going to a V8 and I don't think they're getting to 300k+ as readily as the 4.0L. Also, 4.0L models don't get the best mileage anyway and going to a V8 will likely make it worse.
You could get a really nice Cherokee (not Grand) in that ballpark also. Depending on the t-case, some of the Grands are always in Full-time 4x4 with no 2wd drive option. I prefer to be in 2WD unless I need more traction. I have always liked the XJ body style a bit more and there are fewer electric "doo dads" to have to worry about fixing as it ages. I like simplicity, Cuz I is simple.