That would be Spacenet 3, Spacenet 3R then GE-3 before the rename to AMC-3.
man, I'm old!
This one got me really doing some research. My list that I posted a link to above only had the sat as S3, not S3R, although I knew that Lyngsat had been calling it S3R before it was retired. So I decided to go back and check to see when it actually changed from being S3 to S3r. I looked at Lyngsat listings back to 1998, and they always called it S3R, while my old Westsat charts always listed it as S3 all the way through to 1998, when my subscription stopped. I looked in the Space-Track archive, and they don't even list a Spacenet-3 at all, which would indicate that it never made it to orbit.
So I went back to an old 1987 book I have, Mark Long, World Satellite Almanac, and it had the answer.
Apparently Spacenet 3 never made it to orbit. The 3rd stage failed, and the launch team destroyed the sat during the launch. I'm not sure why the Westsat charts called the sat S3 instead of the correct S3R, because they used the "R" term for other replacement sats.
Also, I've made a couple changes to another chart I posted a while back, ie:
http://www.eskerridge.com/bj/sat/tvrosat4.htm
When I first posted this, there was some question about G28 having ben temporarily called G27. I had that in there because the federal web page showed that, even though I was pretty sure it was wrong. I've done lots of googling, and can't find any indication that this ever happened, so Space-Track must be wrong. I took that out. Also deleted G27, since it's moving now. But this page shows names that the current sats once had before their current names. The only issue, is that some sats were given names before they were launched, and then changed names before they were launched. This was true for a few of the AMC sats, ie several were already in orbit as GE sats, then changed to AMC, while some others were named GE while still on the ground, but had their names changed before launch. The federal web page had the pre-launch GE name in the database, so I have these sats also listed as having been GE sats. The best I can figure is that GE-1 thru GE-8 were in orbit as GE sats, but GE-10 thru GE-12 were GE sats on the ground, but AMC sats upon launch.
Another thing I ran across, again relating to AMC3, and the historical name for the slot, is that the SES company used to be SES Americom, which used to be GE Americom, which used to be RCA Americom....
Well GE Americom used to own not only the GE sats that became the AMC sats, but GE Americom also used to own Spacenet 3, and also S1, S2 and S4 (and also the Satcom C sats). Before that, the Spacenet sats were owned by GTE, so S1 and S2 were originally known as GTE Spacenet sats.
SO, since GE Americom owned both S3R at 87 as well as it's replacement, GE3/AMC3, it seems even more logical that AMC3's slot should be called S3, not W3. The Westar company that launched W1 thru W5 sold out to Hughes, which owned the Galaxy sats.
Anyway, probably not of interest to anyone, but I never realized there had been so many ownership changes of these sats. I had a good time researching all this, as back when I was tuning these sats in, I had no idea of who owned the sats.