power steering pump upgrade advice please

Hi folks.
Im struggling with turning the wheels when hardly moving and wondered if there was a more powerful power steering pump than standard that might help!!
I have a 300tdi disco engine in my 90.
My fluid levels are good, have a recon 4 bolt steering box (changed twice now), have a new aux belt fitted and 265/75/16 stt pro tyres .. but when its struggling you do get that horrible whining noise right at the fullest extent.
Any suggestions would be appreciated

Something is amiss as my 300tdi turns easily .. one finger.

You might have changed the box but maybe the pump is knackered or you have an air lock in the system.
Maybe the ujs have siezed up on the steering column.

Anaconda said:

You might have changed the box but maybe the pump is knackered or you have an air lock in the system.
Maybe the ujs have siezed up on the steering column.

Click to expand...

all worth a look. Thanks

You should not hold on full lock whining, back off a tad and unload the system if you want it to last.
Pump may well be your power issue.

Collapsed rubber hose on suction side, looks fine but internal limer has delaminated causing oil starvation at the pump.