Cat 257b aux hydraulics barely 2

So I am new on here so I am sure someone has come across this. My aux hydraulics are standard flow at just under 16. However when running an attachment it barely flows. I know that it isn't an attachment issue due to I have another machine with the exact same flow and they work great. Trying to diagnose the issue before taking it to the dealer. Thanks for helping in advance.

Hi, a serial number always helps and prevents time wasting and mistakes
is this machine new to you?
is the machine making high idle (about 3240rpm )
do the lift and tilt work OK?
what is the machine your comparing to?
have I read correctly and the machine is standard flow?
Are the work tool couplers compatible and fully opening when connected?
could you do a basic flow test of the system please for baseline figures
Warm up the hydraulic oil by cycling the lift and tilt cylinders leave the bucket on the machine or add some weights of about 450kg's
with the bucket at its lowest level and machine at high idle, fully raise the lift arms and time the result
should take about 4.8 seconds +/_ .5 second
this will give us a starting point
Mark