4.5 litre 89 sedan deville. Stumbles and hesitates only when transmission is in gear. When driving down highway or taking off the car will stumble and hesitate but when I put it in neutral the engine runs fine. For example I was doing 40 mph and it started to stumble so I immediately put it in neutral and the engine ran fine. Is there a switch on the transmission that I should look at replacing to resolve this problem? If this was an ignition problem then I would think that when I put it in neutral the engine would still stumble but it does not. It runs perfectly. Any Cadillac specialists out there that can tell me what is going on? Replaced, wires, egr, plugs, rotor, distributor.