Unless you have 12v accessories to run the only thing changing to 12v will do is take money out of your bank account. If your cables are properly sized, all cable ends clean & tight, the starter sound, the battery good and the truck tuned properly you should light her up in just a few seconds of cranking. Dan is correct, cranking for 20 seconds continuous will unduly heat the starter. Get a new battery (buy or borrow and pay attention to the CCA rating) and try it again.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.