When you start the van it runs normal but after about 10 minutes the idle deteriorates and the van starts gasping for air and eventually stalls and as you travel this will sometimes happen and sometimes it will run fine. If you give it a little gas at a light it runs fine. I replaced the plugs,wires and breather valve and no change?
The mechanics here will know better, but that sounds a lot like the way my old cars with rust in the fuel tanks used to behave.
The Idle Air Control valve may be dirty/defective.
The IAC valve controls the engines idle speed whenever the gas pedal is released.
Sometimes these IAC valves are effected by engine heat where they fail to go the proper position for the idle condition.
What does the air filter look like? If it is dirty a new one is cheap and easy to replace
IAC valve a possibility. Also deposits in the throttle body, making the throttle plate stick closed when it should be ever so slightly open.
That only applies to electronic throttle bodies.
Manual throttle plates close completely, and the IAC valve allows the idle air into the engine.