I have a 1991 ext cab 4x4 1/2 ton pickup with 244000 miles. Just recently I was towing a boat and a clicking noise was coming from under the truck only when going up hill or accelerating.

I put in new universal joints on the rear driveshaft; I thought this was a sure fix, but no.

I also noticed noise is there when I down shift pretty hard.

I don't know if noise is transmission or rear differential. In my mind I have ruled out front drive shaft.

Does anybody have any suggestions?

UEF2

 

hows your front universals. i have a one piece driveshaft. my front universal joint went bad but all the sound came from the rear. mine ticked when i had a strain on my truck

 

thanks for the suggestion, my truck has a separate front drive shaft. I think I will take out the rear drive shaft and drive the truck in 4Hi. I'm now wondering about the transfer case chain or belt whichever it has.