I have a 97 F250 7.3 power stroke. The cruise control works intermittent. It will work fine for 35 t0 50 miles then shut off. I start it back up and it may work 2 miles or 20 miles then turn off again. I also noticed a spike of 100 to 200 rpm's for a few seconds when driving 75. I replaced the brake switch but it did not help. After not driving it for a month, the transmission was slipping in drive and shifting hard. I had the transmission rebuilt and they also replaced the cam sensor and vss sensor. I just went on a 300 mile round trip. Cruise control is still intermittent, had a few spikes in rpm's and once on the way out and once on the way back it shifted into overdrive by itself. What can be causing this?