Brake Electric Antilock problems of the 2003 Jeep Laredo

I own a 2003 Jeep gc Laredo. I have had the Jeep a little over a year and it only has 8000 miles. Everytime I brake if the vehicle is going over 40mph the vehicle begins to shake intensely when I hit the brakes. This has been going on for a couple of months now. Luckily, I dont do much highway driving but I did the other day and it scared me when I had to hit the brakes. This is very odd for such a new Jeep w/ low miles to be having problems like this.