Q: CEL transmission slipping

My truck is a carpet cleaning truck. And I am not sure if my equipment has anything to do with the problems I am having. But I have been getting this code: P2534 - ignition 1 switch circuit low voltage - off and on for months. When I am driving 45 mph my engine was at 2900 rpms. Is that second gear? I had not used my carpet cleaning equipment after the code was cleared the last time. When I drove up a hill my transmission slipped. I let off the gas and it feathered a little until it shifted back into gear. It was fine after that with no Check Engine Light. But today as I was driving down the freeway, and I hit a bump that caused the transmission to slip again. When it shifts back then the Check Engine Light comes on. Then approximately 10 minutes later I was at a stop light. When I accelerated it didn’t go into first gear. I am stuck in whatever gear it’s in. At the next stop light I turned the van off then back on, and it shifted OK until I got home. What’s causing my truck’s problems and how can I fix it?