Multiple Misfires

[nightowl]

I have a 2003 silverado z71, 5.3L , auto trans, no mods, 75k miles. I was towing my boat in Northern Mi. in 3rd (not overdrive) using the cruise. As I was desending a hill there was a slight jerk and the engine light came on. It stayed on and everytime I desended a hill with the cruise on it would start flashing. I crossed into Canada and had to take the cruise off. The engine light stayed on but did not flash at all when desending a hill. When I returned to Mi. and started using the cruise it started flashing when desending a hill and did this all the way home. I had the code read and it was multiple misfires. Why would the cruise cause the flashing? Should I start with plugs and wires or check coils?

Thanks for any help.