Sorry for taking so long to get back on here. We found the issue. We had the Linde service truck come out and he had the problem sorted out within 1/2 hr. There are several lines to the throttle body/mixer and at least one of these lines was almost plugged solid with waxy oily crud. This was causing the intermittent stalling, because when you plug the small line or pinch it off the unit stalls. So when in operation the crud in the line would at times melt/run and plug the line but then open again. All it took was a coat hanger and some brake clean and flushing the line and we are up and running again. Happy Now!!!! Thanks for all the help and suggestions.