1997 Pontiac Firebird Engine quits while driving

Bought a 97 trans am in december. The guy that owned it before me put headers on it, and hi temp wires without heat shields, so it melted a few sets of the ignition wires. Spent 670 dollars replacing all the wires and putting heat shields in it, and the check engine light had been on since I got it so they cleared all the codes and told me I needed to drive it for a while to get them to reset. By the way I know nothing about cars. I drove it for about a hundred miles and it ran great. Brought it back to the shop, they tested everything again, everything worked, and they put an inspection sticker on it. It had recently had a problem where i'd be driving it, and out of nowhere it would bog down and shut off while I was driving it. However, if I just waited five minutes it usually started right back up, but sometimes it wouldn't start at all. After driving it for those hundred miles, it hadn't done it once, the mechanic couldn't find anything wrong with it, no codes were coming up, so he said it was fine. That day I started my 760 mile trip from massachusetts to camp lejeune, north carolina, and 75 miles into the trip, after the car had been running perfect the whole time, plus the hundred miles I drove that day before the trip began, I was going about 80 on the highway, not beating on it or anything, in 6th gear at about only 1800 RPMs, and it just quit on me again. Started it up five minutes later and decided to head home and just fly in the morning, and ten to fifteen minutes later it did it again. Restarted it and it died again before I could get into second. Ten minutes later it started and I babied it about a half a mile to a commuter lot just off the next exit. I had my dad pick me up with his flat bed trailer and bring it back home but I still don't know what's wrong with it. Not to mention that the day before this we put a bottle of dry gas in the tank and changed the fuel filter because we originally thought it was just water or crap in the gas. If anyone has ever had or heard of a similar problem any advice or suggestions would be immense.