Tonight I was driving on the freeway and all of a sudden a loud clunking noise under the truck....like something hit underneath....it happened like 3 times....didnt ru n over anything and nothing i could see was under the truck....any ideas what it might be???

 

For clunking , it can be many things..just do process of elimination.
Most common are:
-sway bar/endlinks
-steering components
-ball joints
-shocks/mounts

 

Any strange sounds prior to/leading up to the clunk?

 

NOPE...I will be just driving...it only happens on the freeway....then bam loud clunk under truck....more on the drivers side....it clunks then goes away....then back again 20-25 minutes later

 

How does you're steering feel?

 

what kind of lockouts do you have?

 

that kind of sounds like a balljoint popping/ shifting every once and a while...

does your steering wheel shift when you hear the clunk?

ive been having a clunk under braking lately, and found out it was my lower control arm bushings.

ttyl

 

Clunk might also be an exhaust hanger gone bad (rubber gromit gone and hanger banging against the floor) it might also be the driveshaft bearings going out... hard to diagnose from a distance...

 

I checked everything but everything seems to look ok....I did find one exhaust hanger that was loose and not connected to anything....other that that it was all good....it only did it once tonight driving on the road....the only other problem was I went to change all my tranny and diff fluids to red line tonight and saw that the previous owner completely rounded off and destroyed both the fill plug in the rear diff and the fill plug in the tranny...tried all night to get them off and nothing.....im hoping that i can get a nut welded on monday to see if that works, but over all i very crappy night.....3 hours of wated effort for what should of been a 30 minute job....hopefully the welding works