1987 shutting off when coming to a stop

[iceref63]

I have a 1987 K1500 with 5.7 FI. Had problems the other day, truck knocked off 3 times in the same day. First time I came to a stop sign. Truck died when I stopped and would not start or turn over. No clicking, nothing not even the wipers or the radio. Headlights work as well as interior dome light. After about 3 minutes and once the starter would spin, it would start up with no issue. Had the same issue about an hour later except it took about 15 minutes before it would spin. Once is would spin the starter, would fire right back up. 3rd time was an hour later but took over 3 hours for it to spin and trn over.

Alternator is fne, puts out around 13.5 at iddle. Not the battery because, when it would spin, it would spin at nornmal speeds. Had it towed home and it starts up fine now. Really do not want this to happen again before getting the issue fixed.

Any ideas as to what to look for? Starter and battery are fine. Battery tests fine under load. Thanks.