alright so whem im going above 45 mph and i put on the brake normaly not hard at all my truck stats to shudder and shake once i get to about 40-43 mph once im under 40 mph my truck is fine is it the shocks in the front or the brakes going out in the back???

 

Could be different things:

- alignment
- wheel balance
- wheel bearings
- worn rotors

This doesn't sound like a shock issue though.