Perhaps you were travelling slow enough for the tranny cooler to not do
its job so well?

Were your tire pressures OK. Low tire pressures will make your vehicle
work harder.
Were you running the AC?
I'm not too  familiar with the Titan, but can you put the car in RWD
mode as opposed to 4WD mode? 2WD or RWD mode would have helped.

On most of the Nissan I know, the tranny cooler is *in* the radiator, so
  all the other influences for the radiator would transfer to the
tranny cooler as well. Given your vehicle's heavy duty capability, I
guess the tranny cooler is its own separate entity, and quite beefy too.

Who knows. Just some thoughts and suggestions.

CD

If you didn't take the trans out of overdrive, or even down to 3rd gear for
hills this will happen.  It is normal, but I don't like it either.  As long
as the needle doesn't pass the line just before the H, you are ok.  But if
you drop the gear to 3rd, more fluid will circulate, cooling the trans.
Check out www.titantalk.com for more information.