Q: turns over, wont start

Bought van a few months ago and had been running fine..One day when accelerating on highway is started sputtering, backfired, acted like it wanted to die. Then it straighted out and seemed ok. Couple days later on the way home from work it did the same thing. Next morning wouldnt start. Got home from work and it did. Over the weekend wouldnt start again. Turns over good just wont fire. Come back couple hours later it fires up...Same pattern since. Guy at work said check fuel pump. I can hear it hum. Put gauge on at the fuel rail and read about 40 when cranking. When it would start it bounced between 35-45. Replaced pump yesterday. new pump kicks on fine, but still no start, just turns over. Took one of the plugs out and grounded against block. Had spark, yellow not blue. Replaced plug came back in couple hours and it started! This AM cranks, no start. I had bought new plugs and wire for a tune up when I bought it so I guess I'll go intstall em. No gas smell, smoke etc

My car has 136000 miles.
My car has an automatic transmission.