I believe that this is one of the cars from Don Shank's collection, correct? If so, this side looks like what Vic Stone classified as a D1 body style, with the bottom side board of the top side framing being one large board instead of the more common two boards seen on B and C bodies.
There were only a handful of D body cars in that collection: 5667, 5538, 5841, and 5674. There was also 5645 with a special side pattern (two boards butted together at the top of one side of the car vs two boards with a slight gap which was standard for D body cars. 5674 and 5841 are on the C&TS, and 5667 became a parts donor after the B end went to the Best Western in Alamosa and the car deteriorated, so that only leaves 5538 and 5645 as likely suspects.
If it's 5538, then neither of the two top side boards on either side will touch (although there may be a narrow infill strip), but 5645 has no space between it's two top boards on one side of the car.
As Dave said, if we could get some other side pictures, it would help to ID, but, to my somewhat untrained eye, this looks like 5645 - which if so, is a 100% unique car as body style S2. However, the lack of a separate number board on the lower left of the carbody (unless it fell off or removed), would make the car more likely 5538 as the 5645 had the final style 6 lettering added with the flying rio grande, whereas the 5538 only had style 3 which would have been painted on the wide board on the car with both the number and D&RGW. So, maybe it is 5538 instead?