drove it a few days and now it will not start?

I updated/tuned up all gaskets, seals, wiring and hoses etc., on my truck, put it all back together, drove it a few days and now it won't start. It does crank over though. I replaced the battery and still no start. Double checked all my connections and I don't see a problem anywhere. It has a dual gas tank, and one didn't seem to work right so I also changed fuel pumps filters etc. I don't understand why It ran good a few days and now even when I try to jump it it still won't start. Battery is good! Any Ford People out there please help me!