Rough running..

[clutch520]

I have a 2002 F350 4x4 CC, auto, 7.3. Idles fine. Pulls fantastic. At slack throttle, say cruising through town at 30-50 mph, the truck acts like it has a miss. Kind of bucks and jumps and get 200-300 rpm difference on tach. Does not do it on cruise control, only foot throttle. Ford dealer had it for a day and said there were no codes, but they did notice the problem on diagnostic computer as a 10-12% variation in throttle. Couldn't offer me a fix tho. Could my throttle switch be bad without sending a code? I heard someone else on here refer to an updated 'fuel spring'...could that be it? Truck has had converter removed before I bought it, and Ford technician thought that could be playing havoc with backpressure sensing on ECU, but it just started about 5000 miles ago, and I've owned it for 60,000 miles. Any help would be appreciated.