1990 Chevy Suburban will not restart after being driven

I have a 1990, 2500 suburban silverado with approximately 139,000 miles. The vehicle runs fine and I do not have any problems with performance. However, after the vehicle has been driven for a measure of time (greater than 20 minutes) and then shut off (to run inside a bank, put gas in, or some other sort of quick errand) it will not restart immediately. After waiting for approximately 15 minutes, then the vehicle will start as if nothing was wrong (seems as if something had to cool off). Power is still evident as all other electrical items will work. The battery is new. Does anyone know what could be the cause of this? Is it the computer?