2002 Jeep Liberty stopping

There are quite a few things that could give you these symptoms Susan. Check to be sure all the wheel lug nuts are torqued properly (100 foot pounds) Your brake rotors may be rusted or out of round, this would give you a pulsation when braking, worse at higher speeds, but usually happens every time you brake.
You may also have worn (loose) steering componets, tie rod ends are fairly common on your vehicle. My most recent employer was a Chrysler, Dodge & Jeep dealer, we replaced quite a few tie rod ends on Libertys with less miles than yours.
Ball joints in your suspension and wheel beaings are also possibilities.
Sorry for the long list, I did put in most to least common order according to the symtoms you posted.
Hope this helps, let me know.
Dan