Transmission is slow to shift until warm-up. The fluid check seems high.

What is your question?

My Solara has 30.000 miles on it. Normally it will shift into 5th gear when it reaches about 35 mph. Then the tach will drop to about 1600 rpm. recently it will not do this until it has been driven for a warm-up period of about 5 to 8 minutes. I have checked the transmission fluid level and it shows above the high mark on the stick when hot or when cold. Could this be the problem??