2005 Ford Escape

Engine Performance problem
2005 Ford Escape 6 cyl Four Wheel Drive Automatic 97,000 miles

I brought my vehicle to autozone and they told me the problem, was that I had coil packs, A and C, that were bad. I replaced the coil packs, but the car still runs unsatisfactory. When I get to about 40 miles an hour, it will start shaking and I have to let off the gas in order for it to stop. However, if I am on the highway and going about 80MPH, it won't shake. What do you think it could be?

Thank You
June 30, 2010.

Could be dirty fuel filter or clogged fuel injectors restricting proper fuel flow. Is engine light on?

Jun 30, 2010.
Yes, the check engine light is on. I already paid the money to get the fuel injectors taken care of. I know the 2 cylinders are misfiring. Could it be an electrical issue? If so, any specifics that you could think of?

Jul 1, 2010.
Since 2 are misfiring and the coil packs are good then it could either be the spark plugs, plug wires or yes even electrical wiring to the coil packs that are not hitting.