4Runner transmission problem

Describe your problem.
I have a 1994 4runner se5v6 4 wheel drive with 203 k miles
the problem is the trans will not shift into high gear until it warms up, usually about two miles of drive time. After this "warm up" the transmission works fine with no problems at all. I serviced the trans about 5000 miles ago thinking this was the problem but no change
What can I look for or do to fix this