this morning, after leaving dentist, truck would not start. Dash lights were on, radio on but nothing from the starter. After fooling with the shifter, (automatic) it started fine. Got home, same thing but could not make it start. Any ideas? Is there a switch for the shifter?

 

it may be the passive antitheft system.

 

Automatics have a neutral safety switch which "closes the circuit" to allow cranking when the shifter is in park or neutral. That should be checked since fiddling with the shifter allowed it to start once, or possibly the shifter linkage needs a little adjustment.

Another possibility is that moving the shifter was coincidence and that the ignition switch is making intermittent contact to the starter.

Of course, Mr. Battery needs to be checked UNDER LOAD; just because radio or lights come on mean nothing.

Question: do lights dim when you try to start it (should, unless the electrical circuit is not being completed) ? Better test is voltmeter across the battery terminals while trying to start, and post that voltage.