Vehicle lose accerleration/decelerates; Slip Light Indicator lights up.

What is your question?

Drive distance is about 25 miles. There's no problem while driving up to 35 mph. Periodically, vehicle hesitates in its acceleration above 40 mph. Slip light indicator will light up for a few minutes during the period of non-acceleration. After light goes out, the vehicle will accelerates to the required speed. However, when foot is off accelerator and tries to reengage the speed, the vehicle coast (decelerates) and slip light indicator lights up again. Any assistance you can provide would be greatly appreciated. Thank you, William G

What makes this problem better or worse?

Nothing seem to make it better or worse

How long has your 2008 Toyota Prius had this problem?

Two Weeks