A little background. 67 coronet 500 3834bbl. Engine and trans rebuilt along with 323 suregrip and u joints. All done in 2010, by professionals, installed by me. Beginning of season last year I was noticing a clunk as it shifted through the gears, trans had a shift kit installed. Didn't give it much thought. Greased ujoints checked fluids all seemed good. Noise remains. This year weather was nice. Took it out and noise is worse. Checked diff fluid, low. Pulled third member out nothing out of ordinary found. Reinstalled with additive same problem. Pulled pan on tranny. Nothing but clean fluid. No debri in pan. Checked ujoints when shaft was out seemed ok no resistance found. All mountings seem tight. Worn but not moving. I'm out of things to check. I have a short video but not sure how to post if even possible. One thing I found today while running it was the driveshaft is extremely warm near the tail shaft of trans, but at the differential is cool. Help!