I'll take a stab here and say it might be your voltage regulator. Two phillips screws hold it in on the bottom of your alternator.
If those brushes aren't making good contact, then this certainly will cause missing/stumbling that you're experiencing.
It happened to me for awhile -- my car would just conk out while idling, usually when hot -- then one day it quit altogether leaving me stranded on the fwy.
It's at least worth a look, and if it's worn but still functional it might be good "run insurance" to grab an extra for when it does fail.
'91 300E, 215K miles