So it won't turn over at all?
If you have an ampmeter try puting it around a spark plug wire to see if you are getting amps. If no then try puting it around the starter, see if you have amperage going into and out of your starter.
basically wherever you have amperage going into, but not coming out of will be what has failed.
Also another thing it could be is your battery.
Just cuz you read 12 volts doesn't mean the battery is good, it may not be putting out enough/any cranking amps.
If you hook jumper cables up to your truck from another car does it start?
If so your cranking amps and battery might be toast.
I know Kragan has a tool they can bring out to your truck and they can test your whole starting system including battery cranking amps.