Those trucks didn't have a crankcase vent filter. You could add one by getting the cap off of an 11-up truck, and pulling a plastic thing out of your breather housing and throwing it away. Install cap and filter off later era truck, good to go.
P0087: Take one of the banjo bolts out of the fuel filter housing. Remove the banjo fitting from the fuel line. Disconnect the fuel inlet banjo bolt and tube from the injection pump. and install the banjo bolt and fitting from the filter housing. This is your test port.
Put a boat fuel tank full of clean diesel in the cab of the truck, run the inlet and return lines to this tank. Find a big hill and hold the truck to the floor while you accelerate all the way to the top. Bonus points if you're running heavy. The point is to run the truck with fuel going directly to the pump with no restriction whatsoever, including the fuel filter. If you successfully make it up the hill several times without going into limp mode for low fuel pressure, then it's safe to conclude there's a fuel restriction somewhere in the supply side. Check every single fitting and adapter on the primary fuel system, including the banjo bolts, check valve, etc on the filter housing, and the 90 degree fittings screwed into the top of the fuel tank. I have seen junk in every fitting. Every single fitting is suspect, so check them all. Some trucks have a screen inside the inlet of the injection pump too, look inside with a flashlight.
If the truck does take a steaming dump, put your hand on the small metal line banjo-bolted to the front of the fuel rail. Is it hot? Does it feel like liquid is rushing through it while the engine is running and actively in limp mode (the limiter resets if the engine is cut off)? If so, the rail limiter valve has popped off. This means there was a spike in pressure (P0088 usually accompanies this) that caused the limiter to pop off. This is usually caused by a sticking SCV (suction control valve, aka fuel pressure regulator, located in top of injection pump). If the limiter pops off too many times it gets damaged. Consider replacing the SCV and the limiter. But first, call your dealer and ask them to prepare you a DX report (if they hooked their computer to it, it saved a copy). What I want to know is what the max fuel temperature is. If we're approaching a number over 210 degrees or so, the injection pump has a high rate of internal leakage and may fail sooner rather than later (most of the ones that fail have high fuel temps recorded). If this temperature is below this range, replace the scv and rail limiter. You need to get the part and serial number off of the injection pump to get the correct SCV (prepare for the parts dept to screw this up). Be aware that the limiter has a thin copper washer between it and the rail that must be replaced, and you need a torque wrench to install it correctly. Something ridiculous sounding, like 108 ft-lbs. I'll have to look that up, that number is inaccurate until confirmed.
Edit: Don't go unscrewing stuff on the fuel system of these things with the engine running. Fuel pressures peak at around 29,000 psi, which is plenty enough to inject diesel into your bloodstream. Do a Google Image search of 'high pressure injection injury' for an overdose of nightmare fuel.
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