SO I am rebuilding the TH400 in my 88 V3500. It sits behind a very mildly built 454 and used for towing 10K trailer loads frequently. I plan on a new larger tranny cooler, pressure guage to go with the temp gauge (pump failure killed this one) and the basic rebuild with new seals and friction plates. Would you run a synthetic fluid or what? Should I remove the "in radiator" part of the cooler routing or leave that for cold new england runs? So far I just have a basic rebuild kit. Anything else you would do while in this thing? My convertor was replaced with the motor work about 10K miles ago. Leave it alone, or replace with a higher than stock stall or.....?