Pearl put out this kit in 1985 (1985-1988). This was Pearls top of the line kit at the time.
The GLX has a six ply maple shell, with excellent hoops, quick release lugs that are made with solid brass parts (yes they were expensive) and superb hardware. Pearl built this exceptional kit to break into the US market of high end drums.
I talked with a Pearl representative in Japan several years ago. He told me that Pearl discontinued the GLX series because the production cost was too high and most buyers, at the time, were looking for a middle of the road, inexpensive set like Tama or Ludwig was offering.
I bought my kit in 1985 because the quality was obvious. I still play it and have never had issues with tuning or rattling.
Eric Singer, the drummer for Alice Cooper and the current drummer for KISS, has used his Pearl GLX kit since the 80's. In 2010, Singer had his GLX kit refinished (after 25 years) so he could use it on the 2011 KISS tour (google it!).
Today, the closest kit to the GLX is the Pearl Masters Series and those come with a hefty price tag. If you can find a GLX kit that has been taken care of, and someone who is willing to part with it, I highly recommend you buy it. You won't be sorry.