Liam Harrington

So just bought a 88 f150 and from 60+ mph there's a constant thump under my feet when I'm on the throttle and when I let off at say 65 the thump speeds up until I get to about 55 then its a smooth ride again, any ideas on what I should look at?

justintendo

driveshaft?

91f150300ci

My 91 does that! I was thinking driveshaft/ u joints, but was told could be the radius arm bushings being warn.