On my 1993 F350 7.3 Diesel I have an annoying problem. The truck is auto with a 3.55 rear end. Everything under the hood has less than 10,000 miles. As I am driving around town my tach shows that I am running at 1100 to 1200 rpm. The engine seems to load up and stumble. If I drop down a lower gear and step on the pedal it will go away. Is this being caused by not enough pressure from the fuel pump or the fact that I put these 3.55 gears on the truck. I did this hoping to increase my MPG. Thank you

 

Pre-Power Stroke Diesel (7.3L IDI & 6.9L) - Ford Truck Enthusiasts Forums Here is a link to the page for your engine.
There is an interesting thread there from a guy who changed from 3.55 gears to 4.10 and got a uesful increase in MPG.
Your problem may be the gears but maybe post on that page and see what the guys there say.