i've got a 1993 f250 that the wipers run slow when its cold out. the wipers run at a decent pace only when i put the switch on high. i opened up the wiper motor case and looked around for grease that had gotten hard and everything seemed ok. sometimes the multifunction switch has some slop in it and is reluctant to run the wipers, if i jiggle it a bit it takes off. in the summer i still have that but the wipers run at a faster pace.