It's made from Ishiwata 4130 tubing and has Shimano Deore DX shifters, hubs, cranks, front brakes, and probably the BB - I haven't pulled it yet, so not sure. Strangely, for a bike with "DX" in its name, it's lacking two DX parts; the Mountain LX rear derailleur and an Exage chainstay brake.
I guess you can get super picky and say there was no DX U-brake, at least there was never one with a "DX" sticker on it. There was a U-brake with the part numbers MT63 and MT62 which is similar to other DX parts, but it said "Deore" on it. They did the same thing with the DX crank too - it never said "DX" on it, just "Deore." Go figure.
So - is this a '90? There are two very strong markers indicating it is. 1990 was the first year for the 'oversize' headset, which was 1 1/8" instead of 1". Several manufacturers maintained the 1" headset right up to the mid 90's, but certainly nobody ever went back. 1990 was also the first year for the Shimano Total Integration shifters, so it's seeming very likely.
However, by 1990, chainstay mounted brakes are virtually unknown. I have a Norco catalog from '90 and the Bush Pilot still had them, but no Rocky Mountain had them anymore, and it doesn't look like Specialized was using them either.
1988 feels like a better number to me, apart from the oversize headtube and STI shifters.
Anyway, I had bought this as a potential Cheap Bike for the 2026 contest, but now that I've dug into the mysteries of it, I'm not sure I want to mess with it.