My remote arrived today, and even came with instructions. They were effectively the same instructions posted by @JLH911 above. The remote feels solid, and appears to be good quality. No problem pairing the remote from original post eBay link. (...once I found the pairing button. It was easy to see the button when I shined a light under the driver side rail of the driver's seat.) I'm fairly excited to have a working alarm, even if it is 20 year old tech. So this is ABSOLUTELY worth the $15 to me!
On the downside, the range is almost as poor as most have reported the factory system. It may work from 50' for me. Time to research "grey wire mod" and find how to improve the antenna. Also as previously mentioned in this thread, the lock and unlock buttons both do the same thing. If the truck is locked, pressing either button unlocks it. If the truck is unlocked, either button locks it, and turns on the alarm. I tested that the alarm works because of the next thing I don't like ...unlocking with the key does not turn off the alarm. (I think that's an issue with the alarm system, and nothing to do with any remote.) Finally, I don't think 4 of the buttons on the (6 button) remote do anything on my truck.
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Net opinion: I'm buying another of these remotes, to have two! Thanks for starting this thread!