2001 S10. I have an idea what's going on but not sure if I'm right and no idea on how to fix. Every once in a while I go to start it and all electrical works (radio, windows, lights) but no starter. No clicking, nothing. This usually happens when it's hot outside. I found that if I keep it in park and rock the truck back and forth, it will start. I'm thinking that the transmission isn't registering that it's in park. After rocking a few times it starts up without hesitation. Am I anywhere close on this? If so, what can be done?

thanks in advance