1988 toyota 4x4 v6 wont start after a few starts, sometimes.

new interstate battery, new plunger & contacts in starter, alternator rebuilt. still doing same thing. voltmeter on battery shows over 14 volts charging.
example today, drive it to work & home ( 5kms one way) for 2 weeks straight. Go to run errands do 5 stop starts in apprx 2 hours. Go to do 6th start - just clicks. I am outside Canadian tire - they give me  one of those battery packs to boost it - try 5 or 6 times, just clicks , leave booster on for a few miuntes try again, just clicks, few minutes more same. Give the shop back their booster, try it again just clicks. I roll it down a little hill, bumpstart it, and it starts so I drive home, 3 kms max to get home. Turn it off. See if it will start and it starts 5 times! friend comes over a few minutes later, so I show him - it starts another 5 times!. it could not have recharged a dead battery in 3 kms enough to start the truck ten times, and it is probably still starting.  I have been fighting this problem all summer long and it is very frustrating. it seems to happen when I do these quick trips and turn it on & off 3 or 4 or 5 times in the period of an hour. I am baffled, spending way to much money on it and would really appreciate any clues on what the problem may be. Thanks in advance, very very much for any clues.