Well, it finally happened. Yesterday, my fat lady (99 IS) let me down on the side of the road

Here's what happened: Went to see my daughter about 200 miles from home. While there, I wanted to take the occasion and go check a motorcycle gear store because I wanted to buy something I cannot find around home that they had on hand. Anyway, got there with no problem at all, bike ran normally.
When I got in town, I came through a fairly long 30 mph zone again with no problem. Then I got in the town and through the highways ramps. There, just as I was accelerating on a ramp to get on the highway, she started misfiring and died. It did exactly the same as when I have to switch on reserve, which I did, but then, a look at the fuel gauge told me 3/4 of the tank was left, so I could not be out of fuel. The engine died, so I pulled on the shoulder and tried to start her again: no luck.
I called a towing to get to a repair location and while waiting for the towing, I checked the fuses and wiring, altough, I'm pretty sure that the problem is fuel related. The engine had been stopped for maybe 15 minutes and I decided I'd give her another try. Plenty of power left in the battery for cranking and the battery is less than a year old. Then, she started and ran just as if nothing ever happened! I let her idling for a few minutes while I called off the towing with no problem. I got on and went to the store I was heading to. Been inside maybe half an hour, got out, started again, no problem.
I got back on and went to my daughter who wasn't there, so I got back on after maybe 5 minutes. She started fine, but about 3 blocks away, died again. I stopped (no choice) and waited 10 minutes: she started again and ran just normally.
So I decided to get back on the highway and try to run back home. I got back without any other kind of problem. She ran just fine for the 200 miles back to home. I stopped a few times for lunch and for fuel and she started right back as usual.
I have the stock petcock and I rebuilt it about 2 years ago because it was dripping. I thing the problem is probably in there, but I cannot understand why it would have worked again. Logically, it should have never started again...
I checked the vacuum lline to the petcock, everything seems normal. I opened the fuel tank cap and listened for air drawn in the tank (pinched or clugged vacuum line): normal.
I did not have to remove the tank lately, so I should not have caused the problem while working on the bike.
Does anybody have an similar experience or an idea? I'm thinking on rebuilding the petcock or replacing with a Pingel, but the fact that I don't have a confirmation on where the problem came from is a bit frightening. It might be just waiting for the right time to show up again...
