Most relocate the pvc valve to make it easier to get to.

I believe the normal/power button is simiklar tro the ect button on newer auto's. If it is it holds the tranny in gear longer before shifting. In my sisters '95 it did help with hill climbs. She was also able to increase mpg if she used L2 around town rather than leaving it in drive.

For a thorough check I would take it to a dealer, they don't charge that much more than the private shop do anymore, should be under $150. Then decide how much of it you can do yourself, the '93 FSM at the the top of the board will work for your '88, then decide who you want to pay to do the work you can't/don't want to do.

If you don't know the service history of the truck, drain and refill the diffs, tranny, t-case, typical tune-up i.e., plugs, wires, cap and rotor, oil/oil filter, air filter, O2 sensor, fuel filter, check the break/replace if nec., check/replace the tie rods, idler and pitman arms, re-pack the hubs/wheel bearings, check/grease ball joints and drivelines. All of this can be done w/o paying a shop, even by a beginner, as long as they are patient and take their time. The water pump and timing belt should also be replaced(done about every 80-100k), and possibly a valve adjustment. You will want to pay a shop to do these, there is a bit more work involved.

If you pull the intake manifold to get the pcv valve, I would pull the injectors and take them to Carburator Factory on Auburn blvd. It runs $32/injector, they clean/rebuild/balance them. It takes about a day to do it, if you get them there when they open you can get them back the same day.