Audio cassette decks playback too slow

in most cases yes: each deck probably has a flat belt that has aged and does not offer the correct tension to the capstan drive. all parts that touch the belt must be cleaned with alcohol; the capstan pressure roller probably needs cleaning also. usually have to remove some parts/screws to be able to take out/install the belt. replacement belt must be about 1/2 inch shorter in circumference than what you remove. of course power/batteries must be removed before opening case. be gentle when replacing screws and note the types and lengths as these are removed to make sure they go back in same place - low cost belts available on internet after searching ($1 - 3$)