Cranks but no start sometimes

I have a 2001 ram 2500 van with the 5.2 it starts  
sometimes and then sometimes it just shuts off
while driving and then I won’t start again I replaced
the ECM, the position sensor, Magnetic plat in the
distributor, ignition coil I can’t figure it out. If I mess
with the center plug on the ECM sometimes you
can hear the relays and fule pump kick on then it
starts runs good then just shuts off I’ve  tried
replacing all the relays and even today I pulled the
new ECM off and plugged the old one in and it
started right up ran for 30 min then I shut it off tried
to start it again and it just cranks but no start.
Sometimes I get the no bus come on the dash but I
am guessing it’s because I keep unplugging it and  
re-plugging the center plug on the ECM because
sometimes it starts that way. I even Cut off a
harness from the junkyard and soldered a new
center ECM harness in and still the same problem.
I’ve  switched around the relays for the auto shut off
with other relays and I’m still having the same
problem. Please someone help me this thing is
killing me.