Re: BIG PROBLEM Leave it in 2wd!!!
You could check if your hubs are unlocked when they shouldn't be.
Engage 4HI and drive at least 10 feet reasonably straight. Then put it in Park (or Rev. if a stick), leave 4HI engaged, shut it off.
Both hubs should still be engaged. Check this by jacking up front wheel, then try rotating tire forward or backwards by hand. Should only rotate a tiny bit to pick up slack in joints then stop, if both hubs are locked. Do this to both wheels.
If it turns freely (only drag the pads on the disc), then that hub isn't locked, for whatever reason. If one turns harder, but still turns, it could be that the other side hub is unlocked, and you're turning the axle shaft and diff. Look underneath to see if axle shaft is turning. Also, the front drive shaft from T-case to diff should not be rotating when you do this (other than pickup of play inside). If your front driveshaft is the one thats turning, then your T-case isn't really in 4HI, for whatever reason.
About the clunks... if your hubs were unlocked, and you spun a rear wheel, the front drive shaft would be spinning faster, and can hit the hubs hard when they engage. I believe the owners manual points out to try not to spin wheels while engaging (yeah, I know its not your fault!).
Sounds like a real mess in NC. You really need 4WD now!
Post back if you get any more info. BTW... a new Ford auto-hub is $236 at dealer... priced one in December. I have one strange hub, thats different than the other (on the outside, the strange one has 3 Torx screws on cover, rather than 5 screws, like my other one, which is what I usually see on Bronc's). " Rockcrawler" (on this board) says its a newer-style Ford hub, maybe like yours. I took it apart and figured out how it works. Then put it back on.
Good luck, let us know!