1997 Chevy Truck gas in the computer

My truck threw a abs light on the panel while driving and hesitated for a few seconds, then drove fine for 60 miles, at that time, on the interstate at 60mph, the truck jerked hard and died instantly. After having it towed to the mechanic, he found gas had sucked up through the electrical wiring and filled the computer with gas. He said he had never seen this happen and really didnt know how to fix!
We have towed the truck home to attempt to work on it, but really do not know where to start. He said he called a fellow mechanic and they suggested possibly the "spider", or an injector, o ring, etc. What would cause this and where should we start our repairs?
Thanks!