It sounds like we had essentially the same experience! I know it definitely made me feel crazy!

What threw me off is the the "extended cut" with sentry guns was seemingly shown on cable television right off the bat - like as soon as Aliens was shown on cable, it was the extended (or at least an extended version). I don't think that was very common, so it never occurred to me that's what might have happened. They usually saved the special editions for home video sales.