Is the propane regulator freezing up or the vacuum fuel lock if the propane regulator is freezing up l would say first look at the thermostate make sure there there is a thermostate in the truck and it is opening.if that's OK then see if the water lines coming to the converter are cloged there should be water coming into the converter and back out into the block some time the block when gets age starts to scale. and could block the lines and that truck water lines to converter l believe are small about 5/16 next you could have a water pump that the fins are bad and rotted not pushing the water hope this helps.