Well mine's not a 4x4, it's actually lowered 4" but has the 5.4 with intake & magnaflows. Our boat is a 24'er (about 5-6000lbs loaded) and it tows just fine. We don't have many big hills/grades up here, but we've been pleased with it's performance.
With what you're going to be towing....no worries. Just don't expect to cruise up the grades at 75mph.
Good luck with it...
-MOB