To the guy who says that the Ford 8.8" is a weak axle.... I'm sorry but you have absolutely no clue what your talking about. The 8.8 is one of the most highly swapped axles into Jeeps after the Dana 44. You want a weak rear axle? Get a Dana 35. THOSE are weak. Or an AMC 20.
Now, Ford or Chevy? I'm personally a Ford guy myself. We towed a 99" Wrangler with lift, big tires etc all the way from maine to florida and back(it weighs 6500lb loaded with stuff) with a 2003 Expedition with the 4.6L. (which we later found out is only rated for 5000lb) without any problems. The 5.4 is a good engine, but it needs updated. GM, toyota, and dodge all have high 300s for their biggest engine. the 5.4 is only 300. they should bring back the 4.6 in it though. It does pretty well in a 5000lb SUV, so I would imagine it would make fairly decent base engine in a pickup. Better than the 4.0L V6 they use in the Sport Trac anyway.