windshield wiper motor

last September I purchased a 2007 winnebago sightseer 35j. This spring I had to replace the wiper motor. It would run slow or not return the wipers to the starting position especially at highway speeds then stopped working all together. Now the new motor is doing the same thing,its like the motor is not strong enough to power the wipers at highway speeds or high wind conditions. the wipers work fine when the motorhome is stopped or traveling very slow, under 40 mph. I am a new member to RV.net but have read about people with this problem but have never seen a solution. I have lubed the linkage but it really seems to be a wiper motor issue. looking for any help!! Ken