Dt175A,
Just got her running, chain on etc.
Did clutch adjustment by the book (at least I think so) clutch feels good, no slop, etc, started toward the first ride, and when I shifted into gear it killed the engine while holding the clutch tight.
Just trying to push the bike, in 2and with clutch held down, it's trying to turn over.

Put her up on a stand and with clutch lever on the case pulled as far as possible, it still acts engaged.

Any suggestions?

Very common if bike has been sitting and many posts on it here if you search the forum. Plates are likely stuck from sitting.

When you say "no slop" it concerns me... there needs to be free play. That's not your problem but it will create a new problem when you free up the clutch as it will likely slip and burn up.

My favorite (lazy) method is to simply tie the lever to the handlebar overnight. By morning, you can usually rock the bike in gear and break the sticky discs free. Then untie the lever and go.

Otherwise I pull the cover, pull the clutch apart, manually separate the plates, and inspect. This is always the best method.

I guess I should've mentioned, just did a rebuild all new rings, crank bearings, seals, gaskets etc. So the clutch was completely separated a few days ago. Before I put the covers back on I confirmed operation. I thought. Can the stack be too tight? Can just plain old 10W-30, make it hang that badly.

I was just looking for something I had overlooked, before I drain it and the cover off again.

Hmmm... okay... It kind of sounds like maybe the thrust washer behind the basket slipped down and got pinched or was assembled wrong.

But if that happened, it would have never worked.

Thank you Mark!
That is EXACTLY what it was.
The thrust washer between driver and driven disks was left off of one side of the thrust bearing. The bearing was just digging in.
Appreciate the direction.