Will a cougar transmission interchange with an explorer transmission?

It dependsprimarily on the engine in the Explorer, and the engine in the Cougar, and the years of each. If the Cougar is 1989-1997, equipped with a V8 (which would mean the tranny is an AOD - specifically, 4R70W) and the Explorer is a 5.0 between 1994 and 2001, it'll have the same transmission. Of course, if you're taking a transmission out of the Cougar and in to the Explorer, the gearset won't be heavy enough, and you'll just end-up ruining it. In the other direction, you might notice a loss of performance because of the gearing. But, it's pheasible if your options are limited.