SM 420 popping out of fourth

[64RELIC]

I'v had my 64' for 20 years and never had any issues with my transmission shifting or noises.
A few weeks ago I pulled the engine to have the flywheel resurfaced, I could no longer stand the chattering when you slowly let the clutch out, funny what you put up with for years.
The machine shop took 11
thousands off there seemed to be like three darker hot spots but no cracks so it cleaned up nice.
The clutch wasn't worn out but seemed dark and possibly oil fouled so I got a new one.
The pressure plate seemed fine it still had the original swirl marks on so I cleaned it well and just touch sanded it a little.
The pilot bearing in the crank looked okay but I didn't measure it, just a little dab of grease.
The cast iron front over the output shaft, not sure what that's called, I pressed in a new seal and made a gasket to where it bolts to the transmission, there was no gasket there when I took it off. It seemed to have some sealant but no gasket.
So everything cleaned and put back together ready for a ride. Forward reverse in the driveway super smooth clutch action, I'm so thrilled. Get out on the road second gear fine third then fourth pops out of gear, leave my hand on it still pops out, it only stays in if I really hold down on the shifter. That's never happed before. I go in the house and sulk.
Next day with hope and enthusiasm I loosened (a little) the two crossbar bolts, the four trans to bell housing bolts and the six engine to bell housing bolts and rocked the truck back and fourth a bunch of times in the driveway thinking there is some kind of binding or alinement issue. Then short ride on the road pops out of 4th. Go back in the house sulk and write long winded forum post.
Hoping some one has heard of this before. Thanks, Jim