Thought it may be interesting to share info. . .seeing as though they mostly use the GMC C-series.

Worked on a lot of there trucks. The new propane system they use is awesome, they bought the company that makes it, I believe 3 years ago. Direct propane injection. Too many problems with the old propane guys

Not sure if I would call bi-phase awsome. . .have you seen many problems with injectors and fuel pumps/purge relays? I think nearly every truck in both fleets have had one or both done, some several times.

Where are you from?

California, 2 schwann dealers near, the early impco systems blew the air cleaners off, blew the mufflers off, cracked all exhaust manifolds, I believe 5 recalls on the early impco systems. The new direct injection, I have not seen many problems (yet).