My 88 was the same way. The trucks were SLE packaged trucks, with an option called the "super saver package." My grandparents special ordered it this way. Took a fully loaded SLE truck, and took away some options like power windows, locks, tilt column and cassette player.
My truck came as an SLE. 350, 4wd, 3.73s, chrome trim, quad headlamps, cloth seat, a/c and cruise. It was missing tilt, cassette player, power windows and locks.
Not a GMT400, but my 02 was packaged very similarly. uplevel cloth, leather wheel, chrome trim, cd player, ac, but was crank windows, manual locks, no cruise and even a floor shift 4wd (which isn't common in gmt800 trucks)