When was the last time you did a power steering flush? yes, you need it done annually like your coolant. I didnt know this either until my rack and pump crapped itself recently, it cost me.......wait for it.........$1300 to get fixed!
The was mainly because its a V8 and parts are harder to come by.
Im not willing to say if your pump is knackered or not but get it professionally checked by 3 independant mechanics.
The rear suspension could be because of your rear trailing arms (unlikely) unless you've done a heap of k's. Or the rubbers on your shocks have lost their grease.
Like I said b4, get it looked at or you'll be guessing till something breaks!