Yes, 4.0 w/ class 3 tow package has stiffer/ longer leaf springs. Plus it has a transmission cooler. The more heavy your vehicle is, the more you can tow. I'm a 2wd and tried to rent a 2 axle Uhaul trailer one time. But they wouldn't let me, they said if i had 4wd i could rent it. Just more weight, so that the load can't push you around as much. Plus the 4.0 can tow more than the 3.0, and 3.0 more than the 4 banger because the bigger engine has more Torque/ HP.
2004 Ford Ranger Edge 2x4
BAMA Proggrammer, K&N Cold Air Intake, Flowmaster 40 series muffler
3inch lift(front spindles, rear blocks), Cranked Torsion Bars, Throttle Cable Mod, Black Diamond Plate Tool Box, Black "Unique" 16x10 Wheels with a beadlock with 265's (31in) BFG All Terrains, Yukon POSI Grip differential, Badass Black Pre-runner Bumper, Stoptech slotted rotors with EBC Yellowstuff Kevlar Brake Pads.