Sounds like you've checked off all the boxes. Maybe try getting it as hot as you can then recheck compression?
Also, spark plugs ok?

The solenoid isn't the problem. As I said the reg. has 125 psi. tank pressure. That is the reading at the port on the new reg. where the low fuel sensor goes pressure does not change. You can turn it off wait a minute and it will not have any power. Wait 30 minutes and it will rev. and then smother out. I had a 6 series truck 20 years ago doing something similar. It had less than 3000 hours. Finally got ahold of the TIEM plant and found out they had reduced the tension of the valve springs on that model year. Put the old part number springs in it and solved the problem.

Pretty rare but I've seen hoses block flow as well when the inside shreds a little and forms a flap that blocks flow. You could gain information by checking the LP pressure at the intake of the regulator when it's running poorly. It's the 30 seconds that makes me harp on the LP supply.

You do have full coolant level I assume, and nothing is frosting up.

Also, is there an LP solenoid? You might want to make sure it has power in run as well as in start mode, though I'd expect that to cut- out running altogether.

I listed everything I replaced. Fuel filter is one. Replaced tank first. to eliminate a bad withdrawal valve. No double quad rings either.

"Starts and runs fine for a short while then stumbles" sounds like a clogged LP filter. I'd also try a different LP tank. (and make sure you don't have two rubber seals in your Rego fitting)