Why does your Ranger start with a jump but once stopped won't start again or even turn over with a new battery?
Check the alternator. If a bearing is semi-messed up it could be super heating and actually try and stall the motor. It also does not sound like it is charging. Go to an auto part store and pick up a voltmeter. 10-20 bucks. Start the truck and hook it up to the battery. With it off the meter should be registering between 10-12 volts. With it running, it should be around 12+ - 14 volts. If it is, than the alternator is charging okay. Still check the pulley on it with the belt removed to see that it is spinning smoothly.