your lines are actually frozen? gas should be able to get a lot colder than that before it gells up. Perhaps you have water in your gas? you can add a fuel conditioner to try to get any water out of the tank and it will help keep it from gelling up to a lower temp. I assume you have no garage to warm the truck up in? Truckers use BBQ charcoal in a aluminum tray to thaw their tanks if they gell up. You could do the same thing, just make sure there are no flames left