When I'm decelerating from highway speeds in 5th gear my 95 Cobra feels as if it has slack in the drivetrain. It only feels this way when I'm decelerating with the clutch engaged and not when accelerating through the gears. I thought maybe it might be the horizontal shock absorber that connects from the body to the rear axle. The car has 87k miles on the original shocks and struts; could it be the shocks are worn out or is it in the driveline or the u-joints???

 

U-joints worn. Gears have bad backlash.