Grinding sound on full acceleration

[pygothian]

Hi everyone,
I just finished upgrading and repairing the transmission in my cougar sv, but something doesn't seem right. When driving slowly I get an intermittent 'click' sound, and at high acceleration a grinding/slipping sound.

I stripped back the entire transmission.
Cleaned everything
Replaced the diff screw set, upgraded the diff balls to CN
Changed some bearings to ceramic ones
Changed the idler
Altered the internal ration to 1:2.8 with the appropriate gears
Changed the slipper set, and went to a 80T
Changed the pinion to a 23T

The diff is tightened as tight as possible, and then undone 90 degrees as the manual states.

The slipper spring is very tight (maybe too tight?)

Gears meshed at the pinion very tight, with slip of paper between.

Everything greased as it should be - Moly in diff, silicone in parts where the manual says. Ceramic grease on other gears

The motor is a 9.5T

Any ideas what the problem may be. Is it overgeared? maybe going to an 81T or reducing the pinion ?

Thanks heaps for any advice
Cheers!