A few things:
1) That chart is a little misleading and very generic. According to that chart, my transmission in my 02 Trailblazer should have died multiple times, and my transmission in my 07 Silverado should be dead now. Good visualization as to how high temps can affect the transmission life, but don't treat it as hard numbers either.
2) On my Trailblazer I saw the same temperature reading in Torque. I also found that it exactly matched my engine coolant temp. I think it was reading the same numbers so who knows what temperature it really was running at? Fluid never was cooked looking or smelling either.
3) I had 215k on that vehicle and never had a transmission issue.
Now, all that said, an aux cooler can never hurt!