I'm new on here - 1st post. I have a 2003 T250 with 2500 hours that has been an absolute workhorse on our farm for the 4 years I've owned it. Other than a blocked intake in the fuel tank a couple of years ago or so, it has been virtually trouble free - until today. I was heading out to the woods to load logs and the engine stumbled and fell from 1500rpm's down to 750. I pulled the throttle to idle and the RPMs came back up to 1020 like normal. I opened it up to full throttle and it went right to 2350 for a few seconds (accompanied by white/blue smoke) and then stumbled all the way down to 750 to 900 RPMs until I closed the throttle and it returned to 1020 again. Any moderate load causes the missing-stumbling in all RPM's. I finally made it back to the machine shed by letting it "catch up to itself" several times. I checked the primer bulb and it wasn't collapsed - even at high RPMs so I figure the intake/ backflow valve in the tank wasn't clogged and also I can hear fuel in the return line to the tank when I squeeze the primer bulb. Diesel fuel flowed out of the filter drain with and didn't notice any water. Outside temps were in the mid 30's and I use diesel fuel conditioner without fail - even in the summer. All temps and oil pressure normal and there are no "alerts" on the monitor. No odd noises from engine or turbo. Any ideas for troubleshooting appreciated.