Slow wiper speed can be due to a worn wiper motor, but could also be due to binding transmissions(the pivots for the wiper arms). I would suggest removing the linkages from the wiper motor, and see if the motor still runs slow or not. Then move the wiper arms by hand and see if they feel like they are binding.
Verify that you do have a FULL 12v(or battery voltage) at the wiper motor, also.
As to the wiper arms hitting on the hood, that tells me the wiper blades/holders have been replaced with the incorrect replacements that are too tall to fit under the hood with it closed. This is a problem with a LOT of aftermarket wiper blades. The only solution is to get the proper wiper blades/holders.
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Joel Adams
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