Trouble starting the Bronco

I've read some of the other posts about cars/trucks not starting, but mine is a little different. A few weeks ago in Chicago was REALLY cold. My truck wouldn't start one morning. I have a brand new battery in there, and it was cranking but not turning over. So I let it sit until the next day, when it was a little bit warmer. That morning it started right up, and kept starting all day and night. I bought a bottle of Heet in case it got cold again. The next day it wouldn't start. I poured that bottle of Heet in the tank, but it still wouldn't turn over.

Per advice from friends, today I replaced the distributor cap and rotor--they said they may have cracked or something. I replaced both (a good thing, because the points were really corroded and eaten away), but still the engine won't turn.

Now that I've replaced the cheapest parts, where should I go from here? Should I go ahead and replace the spark plugs and wires? Does this seem like a fuel filter or pump issue? The strange part is how it would not turn over one day, turned over every time the next day, and then went back to not turning over. Does this sound familiar to anyone?

Also, if this is a fuel filter or pump issue, where are those parts found? This is a 1994 Ford Bronco 5.8L, with about 190,000 miles on it.

Thanks,
Craig