I would install an electic fuel pump in the line between the tank and the filters. If your filters have a port that you could tap in, install a fuel pressure gauge, prefferably between the filter and the injection pump. This will not help if you are getting air in the suction line from a crack or other defect.
About the easiest way to see if you are getting air in the suction line is to find a piece of clean, fuel resistant CLEAR hose. Splice it in as close the the injection pump inlet as possible and watch the line. Little foam streaks are tiny air leaks which usually do not present a problem. Bubbles, especially larger ones indicate a definite problem. If your engine has a Roosa-Master pump, running out of fuel is not a good deal since the only lubrication the pump gets is from the diesel fuel itself.
As you said, double check your lines for restrictions/blockages. It sounds like you are not getting enough fuel to keep up with demand, especially while pushing a load uphill. If you could load the engine the same while working downhill, does it behave the same way? Also make sure your return line is free. Roosa Master pumps will not work if the return is shut off or severly restricted. Sometimes this restriction is caused by the governor retainer ring deteriorating inside the pump, which clogs up the return line. If there are a bunch of little black pieces of stuff in your return line, your pump (and $1000+) are on their way out the door.
The oil pressure switch for the electic fuel pump is good, although I would add an override switch so that you could bleed the fuel system with the electic pump.
Hope this helps. You could get it running real good on level ground and trade up to a Deere--then I could help you more
