2002 Chevy Astro sometimes charges, sometimes doesn't

My astrovan has developed a charging problem. It had a short in the positive battery cable(would short out on steering linkage when wheel turned to the left hard) but this was (supposedly)fixed. Now it sometimes charges at 14-15 volts, sometimes voltmeter needle goes to red zone and below and battery dies. I removed alarm box and horn. It has new battery cables, alternator(i was told) is charging normally. Yet it acts like its still got a huge short(i think) any obvious things I am not looking at? Coould battery itself be a problem?
as I said, sometimes voltmeter is nice an happy and charges at 14-15, then it'll just start to die.

updated 1/21/10
Fellas, as soon as I get a job, you'll get a donation. For real. This van was my cab for 2 years, now it's my nightmare and I can't get to job interviews because it dies on me. Even when it had a huge short, it charged well. Now the charging system is all over the place. Here now, gone a minute from now.