1992 Chevy Blazer idles rough and dies regularly

So I was driving down the interstate last night. A short 50mile trip. I just got gas before I got onto the highway.
about 10 miles down the road, I noticed white smoke.
i ran down the road. No idiot lights have come on.
i stopped at a walmart to check out the problem and I after I shut the motor off I went to start again. No dice. She turns over fires for about 5 seconds gets real rough and dies out. Ive asked around to some people I trust with cars. Theve said eitheri got bad gas. Or running down the highway I blew a headgasket. I limped it home about 40 miles pumping the gas pedal at about 25mph.
the temp gage never went above normal and now im stumped on what to do. Its a full 18gallons of gas that could be bad. Or headgasket. Or somthing else that I havent been told. Whats ur advice?