BC2500HD

Maybe u joints The thump might come from the slip yoke binding on the output shaft of trans or TC? I think there was a TSB on this? New yoke and special lube to use, from dealer. Dealer did my yoke. Gave it back to me and I had the driveline vibration, as described. Took it back and they did front U joint. Fixed it.

Just finished replacing all my lines...I bought a kit from Summit racing. All stainless and pre bent for $330. Couldn't imagine bending them. Huge task as is. Just wish GM would step up and do the right thing, on this serious safety issue. Most of the worst corrosion was where you couldn't easily see it.