when i hit the brakes at 45 or stay at an even 45mph my rear end seems to hop or bounce.........any suggestions????????????

 

Check your rear shock mountings (upper & lower). My 79 F-150 did this as a result of a left (rear) upper shock mount that had rusted away from the frame. At that point I had severe torsional vibration above 45MPH, when brakeing and occasionally upon quick deacceleration.