Gearbox Whine/grind When Changing At High Revs

[Boss4door]

So peeps i have an NA rb25 with a rb20det box fitted and im stumped and need help before i go ripping out the gearbox and wasting my time

pretty much when giving the car a hit at high revs (4500-6000 and further) and changing from 1st to 2nd or 2nd to 3rd during "fast" changes there is whine or a grind going into gear, but never hesitates (and yes im changing gear and using the clutch correctly)... Now if i was punching it and changed gears slowly it wont grind/whine.... If i punch it and double shuffle it still whines/grinds.... and on the odd occasion while im just cruising it will whine/grind...

The gearbox drives fine and no noise no whine or anything is heard during driving besides shifting Any ideas????

The past owner said he changed the clutch recently and its a heavy duty clutch, ive bled the clutch system numerous times at the master,splitter and the slave the adjustment is fine, the gearbox oil has been changed numerous time with quality oil and when i dropped the oil it was clean as a whistle..... Im confused to weather its the clutch or synchros..... Please help i dont have much time on my hands to much around and im ripping y hair out already!!!

[GTSBoy]

Is it a whine or a grind? Does it do both at the same time or does it whine sometimes and grind others?

[Boss4door]

A heavy whine man not the two at the same time

[Boss4door]

Its quite hard to describe tho

[GTSBoy]

Almost certainly worn synchros. Slow down your shifts or rebuild.

[Boss4door]

But wouldnt synchros hesitate and grind going into gear??? Could it possibly be a throw out bearing or gearbox bearings?

[Boss4door]

Just added some lucas oil to the box and did nothing