stumble & surging 7.5L

[Windsurfit]

I have a 94-E350 with the 7.5L (460). I am having a problem whereby the vehicle will stumble and then surge back periodically at idle. It also does happen under load while driving but rarely. At idle though it will do this frequently. Literally it almost cuts out then surges back. I have had two mechanic shops look at (and work on at my expense) but both very competant shops can't straighten it out. I have had a new distributor (Ford) installed, plugs, wires, ignition module, MAP sensor, O2 sensor, and themostat replaced. I have checked the EGR valve and it holds vacume. I am at my wits end. I have now been told that the Catalytic converter could be partially clogged which just to try this experiment will run me another 900.00 for all the exaust work. I have also been told that possibly the Throttle positioning sensor could be bad. But with this being intermittent I have to question the last one. The vehicle has 94K miles on it. Lastly, I was told by my second shop that the computer (processor) could be bad but that Ford stopped producing these last year in 04 and there are no after market ones available. It could be rebuilt but since this an intermittent problem the rebuilder may not even experience the problem (again 200.00 just to try this out).
I would love to know if anyone has experienced this and may offer some sound advice. I really love spending needless money and still experiencing the same problem. It's so rewarding...

Help...Jeff

[radios]

hi , have the type of problem , 94 , e350 , 7.5 ,54,000 mi , just changed plugs , 7 looked same (tan) one looked white, (looked lean running ) this was on cly#8 ,
changed plug wire , no differance, removed egr and cleaned working ok but tube from exaush to egr was craked (repaired) still no change , chaneged fuel filter, put injector cleaner in tank 2000mi , no help. under load (motorohome) climing hill , intermitly once or twice on a long hill it will just slight skip or mis ever so slightly but when it does it will ping (one time) same sound as in low oct gas. or timing off , at idel it will stumble or skip more often , even through the full power specrum it will skip (and ping) but not as often , I was supecting the injector on the cly looking lean , no codes that I can tell and the MIL never came on ,thanks chuck

[gbic1]

A converter could be easily checked by a compent shop. Was fuel pressure checked? Was back pressure checked. Any codes in system? What about the fuel it self? Tp could be checked with a volt meter if you are handy with one. Ford is notorous for having connection probles in the wiring harness. I used a friend motorhome last year on vacation. It cut out on me 3 tims and was the connector at the frame mounted fuel pum getting loose.