1992 GMC C2500 Truck just stops.

Hi, Let me start by saying I'm not a mechanical expert in regards to vehicles but I understand the basics and can google the details if I need to.

I have the use of this pickup truck which has worked great until recently. I took it into a shop to have some new tires put on and the oil changed. While changing the oil, they also performed a stress test on the battery and told me it should be replaced. I told them I would look into that later. On the way home, the engine just stopped. No sputter, cough or anything, just died. The headlights remained on as well as everything else. I looked for the obvious and found nothing. I waited a little bit, letting it cool off a little, and tried to restart it. It started, took me another 100 yards and stopped again. I had it towed home and started going after the things that I figured would be obvious. As the shop had said the battery should be replaced, I did that, though the starter would turn strong when I tried to start it. I also replaced the gas filter just in case it was plugged. After this, I tried starting it. No problem starting but after about 5 minutes it would stop again. I figure it has to be something electrical as it starts without a problem but then dies when it warms up. When it dies, there is no cough or slow down of the motor, it stops as if I just turned the key back. I figure it might be a sensor or something, possibly damaged by the battery test. Anyone have any ideas? If so I would really appreciate it. Thanks