Yeah man those tvh reg kits aren't very good I'm afraid.

Throw a new reg at it and she'll be right.

Your LPG is bleeding into the engine while standing so your flooding it on initial start up.

Easy way to test this theory is to leave truck running and turn off your gas bottle until it stops then turn the ignition off.

Try it again next morning after you turn the bottle back on, odds are it'll start fine.

That little arm inside the reg gets bent and doesn't want to seal on the chamber port so the gas just weeps through.