I have a 2007 5.9 Mega cab 2500 and the ABS and Parking brake light keep coming on. When the lights are on, the cruise control works just as it is supposed to. But when the lights go off, the cruise does not hold the speed or it keeps jumping up and down.

 

you may have an issue with hub bearings take a look at them and have fun it sucks!

 

Rear axle speed sensor or the tranny's output speed sensor. One of the two is having an intermittent fault. Start there.

Chris

 

Well I had the same problem on my 06 and it turned out to be the rear sensor connected right above the rear diff. There are a total of three. Front tires and that one on the rear diff. If you dont want to take it to the dealer you can check it manually by unplugging the sensor one at a time. When you unplug one get in and pull foward to see if the speedo works. If it works plug it back in and move to the next ect.......... Do that till the one you get to doesnt work. The sensor on the rear cost me about 17 bucks at the dealer.

 

Thanks to all. I will give your suggestions a try and will let yall know the outcome!