The Silverado Trim level was mainly the bright trim work (Chrome) being standard, the upgraded instrument panel in woodgrain or aluminum standard, full gauges standard, pull straps w/chrome buttons standard, lower carpeting with vinyl trim standard. This was based on what came with the Z84 for early years or Z62 in the later years.
Radios, power windows, Power locks, power steering, big brakes etc were all options that were not related to the trim level. It isn't like the bundled trim of today. Example: You can't get the top of the line truck with no power window or locks now, then you could...