Every Ford truck I've used for towing with an OD tranny did this....changing the fluid and filter has always cured it. Don't forget to change the fluid in the torque converter, pull the dust cover from the front of the bellhousing and using a large screwdriver or small prybar turn the engine till the plug on the outermost swell of the converter is straight down. There is a rubber plug in the bottom of the bellhousing pop it out pull the plug and go get a beer.....it's gonna take awhile to drain. The fluid breaks down just like oil will. Like I said this has always cured the stutter. Later Whit PS I know this is an old post but my 01 Screw has just started the stutter in the last week and I've got to change it again (212000 miles I usually change it every 50000 but was lazy this time around and haven't done it in about 75000) but it struck home to me.