another good one to add if you have a truck with the A-500 or A-518 transmission and are feeling and hearing a thumping/clunking noise when going over any kind of bumps check the bottom transmission mounts, i had this happen to me and it drove me insane i accually broke leaf spring bolts from over tighting them thinking thats what was causing it, but the entire time it was the botom transmission mounts, check them with a pry bar first if you get any significant movement replace them and i garantee that fixes the thumping/clunking when going over any kind of bumps.