truck will not hold a charge? put 2 new batteries in it and a new alternator and computer. its a 96 12 valve 3500. it will run for a bit but eventually just loses all power and then will have to jump

It can be as simple as a bad corroded battery cable. Check to make sure, they're hard to spot sometimes when corrosion is inside the cable strands. (Double check) If cables are ok, check voltage on battery without engine running, should be minimum 12.4vdc. Start it up and see if voltage goes higher, if it does, then you can ruleout the alternator. If it doesn't you have a bad alternator, again.