Engine is missing at idle,but not under load. Any ideas

[YOUNG]

My truck started missing and idling VERY rough a couple days ago for no apparent reason. The missing will smooth right out as soon as you touch the gas pedal and the truck will run great. I had the truck scanned and the dealer said that it had 3 injectors that were miss firing, so I changed them out with new ones but it still does it. The only thing that will make the truck idle better(I know this is going to sound strange) but is to crack open the water drain on the fuel filter housing and let some diesel run out the back instead of returning back to the tank. I know that sounds strange, but it instantly smoothes out.

Any ideas???