Check voltage across he battery with the engine off it should be 12.6 volts if the battery is fully charged, now get a friend to crank the engine with a volt meter across the battery the voltage should not drop below 9.6 volts if not the battery needs to be charged and tested. Check that the battery connections are clean tight and secure. The starter should draw about 120 amps initially to pull in the starter and drop to about 80 amps once the engine is cranking. If battery voltage is OK and starter draw is high then the starter or cables are bad. Try "jump" starting the truck off another car, with a good set of jumper cables allowing the other car to run for a little while while once the cables are attached.