When cruise control is set to any speed above 40 miles per hour and then when setting it for any speed between 30 and 40 miles per hour it will kill the engine and the check engine lights come on and will need to put into neutral to restart the engine.
First thing I would do is get the computer (OB2) scanned. This will make it easier to help in the diagnosis. Most auto part stores will do this for free. When you get the codes, write them down and let me know what they are. There are many problems that could create this symptom and without speculating for hours let's try this out first and I'll be happy to help you out in finding the problem.