My monte has been having a problem lately where sometimes between 1400 and 2000 rpm the engine starts stuttering and the tach moves up and down with the stuttering problem. The car idles fine and drives perfectly on the highway it's just in the city at slower speeds it does this. Also if I try to step on it a little I almost have to push the gas pedal to the floor to try and get the rpms up, and then it only gets to maybe 2800 before going back down. The car also started shifting a little harder since this started even though I've just had the whole transmission replaced. The car is a 3.4 with 158k miles on it.

 

Service engine lite on?

 

it sounds to me like your car is miss firing. have you had your catalytic converter checked? i had to replace my fuel filter and cat just recently due to the same issue. bad wires or plug will also make it do this and none of this stuff will trigger the check engine light until a good amount of damage is being done to the engine. my check engine light did not come on till after i was flooring it in my car. not once did my service engine light ever come on. I had new wires put on and the miss fire went away,fuel filter replaced and i gained some power back. replaced cat and gained all of it back and have not seen my light since. my wires were damage up inside the wire so it never showed any spark on the outside which is why we thought they were fine in the beginning. hope this helps!

 

cat converter or torque converter shudder is my guess

you could also have a clogged fuel filter.