best fluid for torqueflite

With the Dex,"2,3," ,and now "premium trans " fluids listed for Dextron,I always heard a thinner viscosity ,for mileage improvements. Being a non synthetic base,doesn't a thinner viscosity lead to lower temprature fluid boiling points? Did some personal research . The best of the non synthetic fluids,broke down at 230/240 farenheit . Synthetic,went 450+ . Saved my Turbo 400 ,for a long time.(Yes,I had a huge trans cooler). I simply don't trust,newer "generic" lubricants. Newer enlightenment,would be a wonderful thing.