My oil pressure gauges is reading good and then all of a sudden it goes down while cruising then will go back up again and down again it does not go below the minimum low mark.. oil is at proper level .After it sits for a few minutes it will read good again and the start to do it again ---oil has been changed more than regular intervals....I have found this is a common problem on the dakotas searching the web. A few have had this problem and the motor went,,, Dealers say it is sludge?????? people are pissed that warrenties are not covered..... What other reasons could be causing this???? why would sludge build in a motor with proper oil change intervals?????