Looks like I'm the first reply, and it's a little OT because it was slightly pre-Amtrak. I'd guess Amtrak inherited the equipment.
I've always liked trains. Years ago four of us took the Southern Crescent (Southern Railway) from Atlanta to Chattanooga and back, just for the train rides. If I recall correctly, the cars were stainless steel or silver colored. My friend Paulette and I insisted on having our picture made with the conductor, and he cheerfully obliged. It was my first train ride and the only one for decades to come. We were amazed that the toilets dumped onto the tracks! No restroom use while at stations, of course. That's been a while ago; we loved it!
I am glad you have this memory to cherish. Several of us have pointed out, though, that neither the Crescent or the Southern Crescent served Chattanooga. So here are some thoughts...
1.The Royal Palm ran through part of 1968 and it was mostly stainless steel though not so much at the end.
2 Do you have any way of tracking down the year at this late date?
3, Is if possible you took some kind of steam engine excursion? They did exist from time to time back then and they were on the Southern or Norfolk Southern RR.
4. This is a stretch but is it possible you took the remnant of the once famed Georgian on the L&N (CSX today)? It was the last train out of Chattanooga, and I was on it, of course. That was May 1, 1971 The last coaches to run on that train were stainless steel.
5 Do you remember whether you left ATL from one of the big downtown stations or was it the small station we have today?
6. Is it possibleo you went to BIrmingham instead of Chattanooga? That would have been the Crescent or Southern Crescent.and an easy way to make a one day turn around.
In my estimation,, I think you took the Royal Palm, as already noted. If you could just zero in on the year we could be more sure.