Disclaimer: This is going to be long and I BELIEVE I've searched everywhere for the answer, but can't find posts with my exact same problem.

So my trusty '74 left me stranded yesterday.

I drove the van to work yesterday and started noticing that it was having a hard time starting. On my way home from work, I cranked it over and thought it wasn't going to start. Starter was very sluggish and would barely turn the engine over. But it fired and I was on my way home.

Had to stop for gas and hoped it wouldn't repeat that again. When I left, it started hard again but DID start.

My last stop before home was the grocery store to pick up a few things. Spent about 10-15 mins inside and when I got in the van and tried to start it, NOTHING! Cycled the key a few times and I either got nothing or it would just BARELY turn the engine, maybe a half a revolution of the engine. I never heard the usually "CLICK-CLICK-CLICK" like you normally hear with a bad solenoid. But luckily we were only 1/2 mile away from home.

After we got home I realized I left the key to our other car in the van. So I turned around and headed back to the grocery store parking lot. When I'd made it back to the van I thought I'd try to start it one more time. BAM fired right up no problem!

So I drove it home scratching my head and parked it for the night. Shut it off, turned the key again and it fired up. I figured one of two things were wrong; battery or starter.

Fast forward to today, I pulled the battery out and took it to the parts store to have them check it. The guy behind counter did a load test and the battery passed. That puzzled me even more.


On to the second problem:
I borrowed a spare battery from work and brought it home to throw in the van just to double check that the van would start with a battery that I KNEW had no problems. Put the battery in and she fired right up. Before I started the van the voltage was 12.7. While the van was running I checked the voltage and it was 12.31! I held the multimeter leads on the battery for a few seconds and the voltage SLOWLY started dropping.... 12.31,12.30,12.29,12.28.....
Since I was doing this alone, turned on the MIN/MAX function on the multimeter, hooked it up to the battery, and then revved the engine up. Checked the MAX voltage reading and it was only 12.50

So my alternator isn't charging?? WTF?!

I replaced the voltage regulator about 2-3 months ago and had the alternator tested at the same time. It checked out fine.
The battery terminals are clean and the ground cable from the batt. to the engine block is clean and tight.

I guess it is entirely possible that my alternator has crapped out in the past couple months since I had it tested. But I want to do ALL the troubleshooting necessary before I have to buy a new one. I don't like throwing parts at a problem when I don't know for sure what that problem is.

Anyone have any ideas or troubleshooting suggestions that I could perform to nail this problem down?

Thanks!