1997 GMC Jimmy ignition switch

When you first start the vechicle it may not start on the first try. The dash lights will not always come on when you try to start the car. If they don't, you can usually turn the switch off and try again. If the dash lights come on, then you know that the car will start. Then sometimes when waiting at a light, or slowing down to turn or come to a stop, it will just turn off. No spitting and sputtering, just turn off. My husband replaced the alternator, thinking that may be the problem, but we still have the same problem. We are thinking that it is in the ignition switch. What is your thought?