Transmission hard shifting

Hello have a 98 4 door LS 4wd 82,000 miles, in the last 500 miles have a problem when drive in highways for more 15 minutes, when exit the highway and run slower, the transmission have a hard shifting from 1 to 2 gear only, the other gears are ok.

This problem don't happen when drive slower or a minnor traffic velocity, when is cold, or similar conditions.

Check the transmission fluid lever, color and heat (when run in highway) and are ok.

In chat with a friend and read in the forums have see this problem may happen for a valve or other actuator malfuntion for heating in the transmission.

Thanks for advance.

Replace the transmission fluid, transmission filter, and transmission oil pan gasket. Use Dexron III fluid and do not overfill, (should take about 4.5 quarts). This should be done every 36,000 miles as a part of regularly scheduled maintenance. If the problem continues, make another entry in this thread. Hope this helps.