Bad Convertor?

Hey guys, do these symptoms sound like a bad convertor? I just finished installing a brand new .040 overbored 350 ci into a '86 GMC shortbed pickup. This is hooked to a 1979 th350 stock long tailshaft transmission. Engine fires up, idles, and runs great. The problem is when the truck is idling in gear while stopped, as if at a red light. The engine almost stalls, shaking and rattling until accellerating to about 1500 to 2000 rpm then everything smooths out until the next light. Cruising down the road with no load on the engine I can feel it be not smooth, if that makes sense. Idle is set at 680 in gear. Cam lift is .495/.510. Timing at idle is 12*. Thanks for any imput

never heard of a non lockup convertor giving such symptoms

Sounds like a tune-up problem to me.... What's the duration on the cam, and how much vacuum is the engine making??? Timing set with the vacuum advance disconnected? What kind of carb, did you rebuild the carb?

Problem with brake on at a stop light?..Maybe brake booster leaking. Hyrdroboost or Vacuum booster?

Hey guys, thanks for the replys. Edlebrock performer carb #1405 rebuilt last year. 17" vaccum. Idle set with vaccum gauge. Timing set with vaccum plugged. Cam duration 211int/221 exh.