Valve body upgrade will help speed up the shifting which in turn does not heat up the trans oil as much, but then again
VB upgrade is only available for the 5AT (at least for now).
An oil cooler will also keep the trans oil cool and help lengthen it's life.
A torque converter upgrade does nothing to longevity. It simply helps with launching and slip.
But as Z eliminator said, the problem is with the clutch packs in the last 3 gears. It's all about driving style. If you're going 60mph in 7th and wanna go WOT, drop it to 3rd gear first with the +/- BEFORE pushing the pedal all the way in. That way, you don't stress the trans and cause premature failure. It will help your trans last longer. For the 5AT, I think it's the 4th and 5th gears that are weaker.