Van sputters on wet days and does not sputter when dry outside. When you come to a complete stop (when it sputters) the van will die.

Did you bay a new one ?

Bad fuel pump, stopped up fuel filter, mabey? First check for vacume leaks.... may try unplugging the throttle position sensor. Plug it right back in... just check the connection.

What about the spark plug wires they would be the likely cause of this problem.

the first thing I would start with is looking for vaccume leaks. be sure to check your EGR valve, then move to your MAP sensor. The next thing that it could be is a stopped up catylic converter

Testing is the way to a fix . Fuel pump pressure testing , electrical testing . Viewing engine sensor data on a scan tool . Instead of guessing as to the problem learn to test or take it to a qualified repair shop . Changing ECU without doing it correctly can cause problems that were not there before . PCM - engine computers need to be programmed , dealer only.
GM Fuel Pump Relay Testing
Testing Electric Fuel Pump Problems with Voltage Drop Test
048 Engine Hard to Start or No Start Scan Data for Starting Problems

I would check the fuel pressure. You could have a clogged fuel filter or a weak fuel pump.

have you had the throttle cleaned? Sounds like your fuel pump may be getting hot and cutting out. Its possible it could be a faulty ignition module,but that usually just causes a no start not a suptter and stall.

take a look at the fuel pump

Have the drive gear on the distributor checked, these are known to wear and cause a timing issue.

Check the egr valve