It's a good looking engine. From my experience there are several major indicators these pumps are in need of a rebuild. It could be leaking fuel, not responding when adjusted, poor fuel mileage. You also have a 4d55/56 expert in Burbank, CA. Mike Warme knows more about these little things than anyone in the country. You can send him an email at www.mikewarme@yahoo.com

As far as an upgrade, I think the pump you have is fine, it just need a good rebuild. I am guessing the injectors, turbo and a few other parts are in need of some TLC.

Spence
1985 Mitsubishi PU 2.3 Turbo Diesel, 13" lift, Watercooled turbo, 4D56 Head, Atlas II,Fox Coilovers, Elockers,

1983 Mitsubishi PU 2.5 Turbo Diesel 4x4, fully restored

2003 G500, sliders, beadlocks, roofrack, ladder etc.