The door shell is the same for all GMT400's.The inner panel is what makes a door power or manual.
If I'm incorrect someone will correct me.
Mostly correct. The door shells are the same for manual vs. power windows; there are other differences in the door shells over the years, though. Best bet is stick as close as possible to your year model for the best fit and overall outcome (most importantly, the fit of the shell to the cab.)
The 1995-up door shells have an indentation above the inner door panel (or "door module" GM calls it) to allow for the interior door handle to slide into place. The inner door panel for those years has an upkick in the sheetmetal for that handle. You can use a 1988-1994 door shell here and hammer a little dent into it for clearance, or even not bother, it just makes the interior door handle a little more difficult to slide into place when swapping out.
The hole stamped in the door shell for the exterior handle changed a little bit in the later years, and it's hard to pinpoint exactly when - and it may have varied depending on which plant built the truck, is my best guess. The later trucks - around 1996-1997, have an exterior handle with a thicker plastic bezel around it, just by a couple millimeters, that make using the old exterior handles tricky as they'll be a very loose fit.
Richard