Why does the transmission have a "hic cup" reaction while driving over 45mph?

Sometimes, it can very difficult to distinguish the difference between a transmission problem and an ignition misfire - as in failing spark plug wire(s) .. Both may exhibit the same symptoms under the same operating conditions .. Engine misfire is often mistaken for transmission related problems! .. Suggest having auto repair shop check it out as it is more than likely beyond the average DIY'ers capability... How long has it been since last tune-up?