Title says it all. Car is highway driven 50 miles a day.

180 T-stat.. definitely.. as for tranny cooler.. I don't know if yours have one bulit it or not.. my 97 SSEI has one built into the rad itself.. most people would say you should run a tranny cooler.. but from some of the research I"ve done.. and the fact I live in a colder climate and I don't tow.. they said a big tranny cooler would actually do more harm.. but thats here say.. if you run a small tranny cooler.. I think that would be fine..( but since you drive mostly on highway.. I don't think you need one. if you are going to mod the shizznitz out of your engine.. then yes.. tranny cooler then for sure.

When I got my SSEi last spring I called the #1 tranny shop in town. They said get the biggest cooler I could get infront of my radiator. Now with 92K my car shifts better than 4T65-HDs with 1/2 the mileage. Do the cooler. Also, I ran mine so it goes in the radiator first, then the aux cooler back to the tranny. The same way my dads 96 Ultra with a stock cooler is run.

Jay

I live in CT and it getts hot enough in the summer to require a cooler.
I installed the smallest 2,000 pound towing cooler on both my cars and
the fluid stays cherry red and shifts like a dream.
Prior to that the fluid would get brown after a couple of years.
Don't know what temp I'm running now but its all good.
Definitely install a cooler if your summers get to 95 - 100 deg. outside temp.
I installed mine like the factory SSEi setup in series to the radiator first then to
the cooler.