I've got an 85 4x4 318, 3 spd 1/2 ton.... after some mild mudding.... trying to illegally cross the Canada/ U.S. border with a new snowmobile in the box, trying to avoid paying extra taxes and duty etc.
... It ended up not being worth it because my truck was not too happy about it. When i got out of the bumpy field there was some clanking, almost like something was tied to my driveshaft, hitting the frame everytime it revolved.

Anyways I made it home fine then the next morning I took my truck out and there was tons of vibration just above 2000RPM's or 45 MPH. almost like i lost a weight on my driveshaft or something. The truck has a 4" lift, I bought it like that so I have no idea what was done in terms of driveshafts or alignment etc.

Ps. I've had troubles with the rear bearing on my transfer case that supports the driveshaft. A couple months ago i had a bearing failure, so i'm thinking it's my driveshaft either out of alignment or unbalanced, anyone experienced with these type of problems i'd be happy to hear your input/ suggestions.

Also I wanted to know what my truck would be doing if I happened to snap and axle or something????

 

When a UV joint goes bad, it starts with a clanking (sounds like a string of tin cans being dragged behind your truck) and no other natable problems untill it worsens, then the vibration comes. It sounds like a classic fail of a UV joint. Drop your drive shaft and 20-40$ should do it.