4 speed to 4 speed od clutch chatter

I had the entire box apart and all the gears looked clean with no wear..The cluster pin is tight still since the box is cast. The leaf springs are brand new espo 6 leafs with around 500 miles..Brand new shocks as well.

The clutch is a mcleod performance diaphragm type with around 500 miles. I had looked at all the fingers today with it torqued down and all even to the eye.. There were zero hot spots in the new flywheel or pressure plate.

The chatter is not gear noise or gear rattle in the transmission..It reminded me of bad chatter of a extreme warped flywheel. It shook the car to the point it felt like it was gonna break something. This wasn't trying to launch the car or anything. Just trying to make the car move made it do it with low rpm or 3k steady and ride the clutch out. 2nd gear I could get it to move smooth but had to work clutch to get it moving. I can't see the springs bouncing trying to make the car move at 1500rpm riding the clutch. I could see doing a full wot pull from dead stop and getting wheel hop and chatter.

Why I come here and ask. Something I have never had happen.I have built 10 cars for myself all stick shift,number of customer cars and had quite a few 4 speeds apart with no issues. I built my own engines, transmission and set up my own 3rd members so have the experience.

I may try the od box in my 68 cuda to see if it does it in that car one of these rainy days. But right now I have to finish my 73 cuda and not going to put the time or effort into a 200 dollar od 4 speed.