There is definitely cross tolerance. Gabapentin is much weaker than pregabalin and also suffers from this annoying inverse dose-response curve where the more you take at one time - the less is actually absorbed into your body. This requires a method called “staggering” doses in order to get an actual sedative buzz (at least for someone with a tolerance).
I would take 300mgs every 15mins for 2 hours or so to get buzzed. Pregabalin doesn’t suffer from this and is much stronger IME. Much more like a ‘proper’ sedative I.e benzos.
However you certainly could switch to gabapentin to taper off and it would probably substitute for pregabalin if you ran out and all you had were gabapentin - just at much larger doses.
I was one of the lucky people who were incapable of developing a physical dependence on gabapentin. I took it for chronic tension headaches at 600mgs three times daily for 4 or 5 years and never had an issue stopping. I heard a lot of stories of people suffering from a pretty classic sedative withdrawal syndrome when they ran out or tried to stop.
I’ve only taken pregabalin a limited number of times, maybe ten or twenty times… my buddy had a script for it long after I came off gabapentin and he would throw me a couple trays every now and then and personally I think gabapentin would be a bit of a letdown coming from a background of pregabalin use. Pregabalin is a much more potent and enjoyable analogue of gabapentin IMO