Truck won't start sometimes

[MarkR]

When I turn the key to the start position I hear the starter kick for about 1/2 a second then nothing. I get the lights and the steering wheel moves but no start. I turn to off then to start and everything starts up. This happens every so often. Here lately once a day.
The dealer has looked at it twice and they can not find anything wrong with it.
Does any one have any suggestions?

Thanks'
Mark