yukon problems starting

My 99 yukon has problems running when it rains or is humid. It will crank, start, then shut off after two or three seconds. As soon as it dries out , its fine. I thought it could be the vehicle kill switch malfunctioning, but now the dealership says my components aren't communicating and wants to replace my cluster. This will cost me $500. and they're not even sure that will fix the problem. What can I do?