A thermostat sounds like a bad idea as that would create a pump problem and fluid starvation problems I'd suspect, besides 180 degrees is too hot for tranny fluid anyways. Granted, too cold of fluid is just as bad as slightly too hot. I'm assuming you didn't put a gauge on it, if you did that would help quite a bit on determining how close you are. A parallel set up would allow for the radiator cooler to do its job and allow it to heat up the fluid as the engine warms. If it is a replacement radiator I'd do this. If it is an original 92-94 radiator I wouldn't as they have a screen in the cooler which can get clogged causing those pump/fluid starving problems. Best high tech advice I'd suggest would be a slice of cardboard in front of part or all of the cooler... It works on my Nighthawk oil cooler. Even have a slick cardboard set up that is painte black with strap ties to keep it in place.
