I can be driving along at 30 mph more or less and my truck is purring like a kitten when the RPM,s jump up around 1000 or more a couple of times and then be fine for several days before it happens again. Has this happend to anyone if so what was the cause?

 

Does it feel like the tranny is downshifting or slipping?

 

I don't think so. I just had my transmission serviced and it is OK. I have a Predator chip I think is doing it. I turned the chip off and it has not done it with it turned off.