R150F rebuild question.

[freeone56]

I'm new to Toyota 4x4 trucks. I now have a '90 TRD SR5 excab 4x4. I am noticing a rumble/vibration in the tranny on the highway in 5th gear. This rig has 270,000 miles on it and I was told the last 100k was mostly highway miles. Thinking about buying a rebuilt R150F for this truck. What are the updates or options I should consider for this tranny rebuild. I'm not a hard core rock crawler but I do like getting up in the back country trails some. (3.4 v6, E-locker)