Hilux 4x4 Forum

Hi I have a 2005 Hilux Vigo 4x4, when engaging D drive or R reverse we hear and feel a thud under the cab. On the pit I have seen that the problem was the prop center bearing cushion jumping up and down when D or R was engaged, I changed the center bearing fitted a genuine part only to have the same problem upon further inspection I noticed the rear springs flex big time when engaging D or R resulting in the diff nose cone diving up and down further resulting in the major flex and thus on the center bearing. What is the solution in 44 years in the motor trade its my first time to see springs flex in this manner, do we add another leaf, rebend and tention or what is the best course of action? Help.