I have the KRK 6" speakers and like them quite well. I wanted something that was reasonably accurate for mixing, but not so clinical that the sound is uninspiring for composition and tracking. The KRK seem a nice compromise between those goals for the price point.
For the OP, what exactly is the problem you are hearing when you listen in your truck? Too much bass perhaps? Whatever monitors you use, you're going to need to practice with them to get a feeling for how the mixes translate to other systems and environments where you music will be heard. By all means, try out your mixes in your car, on earbuds, on your home stereo and your friends' stereos, on a boombox, etc. It could be that a mix that sounds good on your monitors will sound too bassy, or too trebly on some other system. You learn to anticipate that and adjust. Burning CD's seems a cumbersome way to try out your mixes. Personally, I just convert my test mixes to mp3, copy them to my phone, and from there send them to an ipod, to my car stereo via bluetooth, etc.