What I'd do is find the hydraulic manifold and first check all the wiring is in good condition, no broken wires, no corrosion, etc. Wiggle things, unplug and replug connections. And then, my favorite repair method...whack the solenoids with a rubber mallet. It's satisfying and often works to restore sticky valves and coils. The other thing you should do is wipe down the jack shafts with whatever the manufacturer suggested for your model...usually ATF for that age of system. After that, maybe spray them with a lube. The 'LAST' method is cracking the hydraulic tubing for ATF fluid on the 'lower solenoid' as it's going to spray everywhere as it's under pressure.
Of course, it helps to measure that you have a nice solid 12 volts on the big wires going to the electrical items on the manifold.
My Power Gear system was a '94 so some things might not apply, but perhaps my blog article on it would help:
Power Gear Leveling System