Cars speed won't drive up to its normal speed

Check the wheel lug nuts, especially on the front. Sounds a bit like a loose wheel. Could also be a wheel balance issue. A wheel weight may have fallen off. It doesn't seem to take much to make the car shake. If you're in the snow belt like I am and have been using your car as a snowplow, like I do (bad idea, by the way) you may have a bunch of snow and ice built up in one or more wheels. I've had that happen a number of times. First warm day, snow melts and its all good again.