The update would most likely be a CAPS pump replacement and ECM software updated if needed to match the replacement pump.

The CAPS pump does not like an inadequate or air entrained fuel supply.

There have been issues with the fuel hose being misrouted and either getting a kink at the tank outlet or being squeezed between the tank and transmission housing. Later production had a spring installed to prevent the kink at the fuel tank outlet.

Common air leaks are the inline strainer connections and the fuel lift pump fittings, connections and sometimes the fuel pump bolts loosen and allow leakage. Since the lift pump only runs for 30 seconds after key on the fuel leak becomes an air leak.

Keys to look for are an engine that starts smoothly and holds speed evenly without surging or excessive light colored smoke. When these start the idle speed will be 850 rpm for a short time then increase to 900 rpm.

One other point is that the injection nozzles can need replacing yet the engine will run smoothly and make decent power. Nozzles are relatively inexpensive and a replacement set, along with a valve adjustment can really sharpen up an engine. Engine valve adjustment doesn't normally get too far out of adjustment, the valve train is pretty solid.