2003 Silverado Wont Start

I'm hoping someone can help me with my truck problem as my local Chevy dealership hasnt been able to. I have a 2003 Chevy Silverdo Z71 that I have been experiencing intermitent (6-8 times) starting problems with over the past 2 years. What happens is when I go to start the truck the panel lights all come on as normal but the engine doesnt turn over. In most cases I shifted the truck from park to neutral and back a few times and was able to get it to start. However one time last year I couldnt get it to start and had to have it towed. Of course when I got the truck to the dealership it started right up and they could find nothing wrong with it. I have had it in the shop 3-4 times and they can find nothing wrong with it. Right now it's sitting dead in my driveway.. Anyone have any ideas? Someone told me I should have the neutral/start/stop switch replaced. Any advice would be appreciated.

If you are capable, start by checking for 12v at the crank wire on the starter solenoid while someone holds it in the crank position, if none, does the security lite stay on while it will not start.