Hello!

I bought my 1992 D250 5-speed about a year and a half ago, and it's given me zero problems for over 20,000 in that time... until yesterday. Hoping you all can help me troubleshoot a SEVERE power loss/smoking problem, which presented at highway speeds.

SHORT VERSIONthe acceleration dies completely above 2000 (?) RPM, like God is cutting off my fuel. Power returns intermittently, especially after restarting motor. Problem began very subtle and by the end of a 600 mile trip had me chugging up hills at 25mph on the interstate. Motor would stall at idle by end of trip. Difficult to re-start, will eventually re-start pumping accelerator. White smoke like crazy, accompanies moments of severe power loss/hesitation. Motor still runs smooth. It's my only working vehicle, so I'm relying on it to get me 400 miles home for the holidays. Please help!

LONG VERSION:Yesterday I drove the truck 600 miles home from a job-site. Soon into the journey, I noticed a slight hesitation/miss while trying to maintain highway speed uphill. It was so subtle at first, I dismissed it as a hallucination - but soon I realized I was losing top speed- from 80 to 75, 70 over several hundred miles. Except for the loss of power and very slight hesitation, the motor sounded ok and ran smooth as ever.

I pull over for coffee in Ohio (Love the 700 mile range of this thing!), now struggling to maintain 60mph on flat highway- and popped the hood. Few drips from the fuel filter, but nothing obviously out of place under there... then, it WON'T START! Tried it again, got it started when I was pumping the accelerator. Entered the highway one again, and-

A very odd thing happened- full power was back! For a mile- then I felt a sudden drop off of power to pre-stop levels. (This return of power seemed to occur intermittently a few times during the trip, usually after shutting the motor off and turning it back on again)

As the trip continued on (now at 52mph max on flat ground, as low as 29 up hill at full throttle, and dropping) the sun came up, and illuminated the billows of WHITE SMOKE I'd probably been producing all night. The worst clouds of smoke seem to be produced when I'm feeling hesitation from the motor.

A weird trick I found helped me temporarily pick up top speed- Towards the end of the trip, when I was getting desperate for speed, () I found that if I shifted into neutral while moving along (which at this point would stall the motor) and dropped the clutch to restart the motor, basically 'roll starting' it during highway driving- my top speed would temporarily increase by 10mph to maybe 55.

I suspect the following may be a play, but would appreciate all your input so I can hopefully focus on the most likely causes in the limited time I have before I have to drive home for Thanksgiving!

-Fuel shutoff solenoid- can this partially/progressively fail starving the engine of fuel?
-Lift pump?
-Fuel filter? (Replaced 10k ago)

Thanks from Pittsburgh!