SLP, ZZP, and PFYC deal with the Grand Prix market. The GP'* didn't get the 3800 until 1997, which was the first year of the 4T65E transaxle. As such, they have no experience with the 4T60E. The 65 was based on the 60, but has a totally different set of problems.
From a reliability standpoint, the 60 seems to be much more reliable and less failure-prone long-term. This can be improved in a longevity sense by installing a trans cooler. The 65'*, on the other hand, have been shown to NOT have the heat problems the 60'* had, but even without the trans cooler, the 60'* go longer without problems than the 65'*. If you go with a trans cooler, and it'* in your budget, get one with a thermostat so it'* not over-cooling in cooler weather.
Buy the stat anywhere. Just ask for the 180 that fits the stock 195 application. If they don't know, they don't know how to read their book and crossreference. In that case, go to another store. You need the round black rubber seal AND fiber gasket also.