i have a slightly leaking radiator (r.h. side, probly the plastic end cap) that i will need to replace, i have a std trans 4.0 with a/c. any known upgrade, maybe one intended for a auto trans? cools fine except when its real hot out and im towing something heavy, then its running a bit warmer than normal, not overheating but enough over normal to concern me and i'll run the heater on high to bring the needle on the guage down. i have 135,000 on the stock unit, oringinal water pump too. antifreeze has been changed a few times, ive thought about doing the water pump as well, even if my current one is still o.k.