I have a 2003 1500 quad cab. When I am going over 40 and press on the brake it shakes. Cant feel it as much at lower speeds. It is not the rotors I have already replaced them. What else would cause this?

 

Bad tie rod ends can cause that.

 

What could I do to check this?

 

If you replaced them with Mopar rotors, could still be the rotors. I had same issue with ex-wife's Grand Cherokee, new rotors warped almost as soon as I put them on. Went with inexpensive auto parts store set and never had a problem.

To check tie rod ends, lift front tire, look for side/side play...

 

What shakes exactly? Do you feel it mostly in the steering wheel?

 

have you balanced and rotated your tires lately

 

I had the same problem on my 06. Changed the front rotors and brake pads and no more shakes.