If the front is sitting higher than the rear at highway speeds, the airflow under the body will be different than anticipated by the factory. You may be getting a slight "lift" effect as a result, which will make the front end feel light, twitchy. Steering geometry may also be affected by the high front/low back, same twitchy result. If you don't have the factory manuals, I'm betting someone on this board has posted the appropriate front/rear ride heights for this model.