I have a 2004 250 HPDI, and it's starting to idle more rough than normal. When it's in neutral and firing on 4 cyliners, it idles fine. But anytime I put it in gear, it'll idle rough and acts like it wants to die after about a minute of running. It run fine at every other rpm, no loss on top end, starts fine, isn't smoking anymore than normal or hard to start. I run ringfree in every tank, so I'm trying to figure out if it's a simple solution. Thanks.