01 automatic transmission shifting problems

Within the last month or so, i've been having shifting problems. on a cold start i shift to reverse and it takes about five seconds to go into gear and the same to go into drive. Once its been driven for at least 15 minutes it shifts more like it should but its still like it was. What can i do to solve this problem?

Your trans fluid coul be low. The level rises as it warms up. Check that first.

I checked it and added more fluid plus a supplement when the problem first arose. No change at all