[updated:LAST EDITED ON 10-Jan-02 AT 11:35 AM (EST)]I finally got a VERY experienced Ford dealership mechanic to talk to me about this issue. He said we're on the right track with the EGR. The reason it starts happening as the truck ages is because of "coking" on the valve seats (carbon buildup). This, coupled with the introduction of exhaust gas from the EGR, changes the air/fuel ratios just enough to cause the stumble. "You didn't hear it from me" he said, "but if I were you, I'd disconnect the tube between the exhaust manifold and the EGR, put a wadded up ball of tinfoil in there and reconnect the line. The foil will block the flow but allow the valve to function, so the computer will still think everything is working properly, and you won't get a 'check engine' light." He also said that because the 4.9 runs so lean, it doesn't really need EGR anyway. This is also why the 4.9 shouldn't ping after the "operation". Some V8's might get some ping--if they do, then restricting the flow as Nitro94 and Gembeau suggested above should allow just enough EGR to get rid of it. Of course, if you really want to eliminate the cause, you'd have to have the valves ground to get rid of the coking. But that's a whole lotta work when good old Reynolds Wrap will do the trick. By the way, it worked for me!