Well thats pretty re-assuring. Its just during school on the short drives to lunch, I can tell that I drain my batteries when I go to start the second time. With only a 2-3 minute drive, it just isnt enough time for my alternator, so I'm thinking a more powerful alternator, such as the 3G would cure most of that.
It sounds to me that you lack battery-power, more than alternator-power.
The next time you need batteries, put in a pair of Group-30/31s, instead of the called for Group-27Fs; although much larger, they fit nicely.
The Group-30 and Group-31 are exactly the same battery, with the difference being that the 30 has the posts located offset/closer-to-one-side, whereas the 31 has the posts centered on the top.
I prefer the 31s centered posts, but have used both with equal success.
One other thing you can try that will help a bunch is to hook up a locking throttle-cable, with the tail-end having a ball-chain, such that the foot-pedal can easily over-ride it.
I have never fully understood the wisdom of having a diesel engine idle so low to begin with, unless it has something to do with the functioning of an automatic transmission; everything about a diesel fares much better when idling around 1200-RPM, instead of the usual 5-700-RPM.
With the locking throttle-cable, you can kick the RPMs up quite a bit, giving your alternator a better chance of charging things up; with an added advantage being a much better functioning A/C.