History: I've had this tractor a little over a year now, when I first got it, the po showed me how he would start it. Little spray of starting fluid, glow plugs, and start. Now I thought that was crazy. But it is a VERY hard starting tractor without plugging it in unless its above 50* outside. Anyways, its always had this high rpm miss(about 2700 rpm, right where it runs for the 540 rpm pot speed). Well as some of you know, I ran a tank full of used, filtered atf through this thing, when it was running on the atf, it didn't have this high rpm miss, so I thought the fuel injectors and what not could be dirty n the atf was cleaning them out. I ran the tank of atf dry, than did a sevice( fuel, air and oil filters, and changed oil of too) filled the tank with new Diesel, and the miss is now back. What could be causing this? Is it because of the ultra low sulfur diesel fuel? I'm stumped here.