had posted once before about this, found out that if I pull real hard on the shifter lever that puts the truck into 4x4, the clunking goes away...is there a screw or bolt or something that places the shifter into gear, it seems that it is not engaged all the way.
f150 1988 4x4 auto 410 gears 4 inch lift 302 ci

 

If its a borg warner 1356 it could be a bad "hub" inside. You have to open it up and get a new part. Happens all the time. the pump kit is about $20