It may have been covered in the above link, but check that your engine mounts are up to scratch. You may benefit from engine mount inserts too. 

I have a fully rebuilt Gen 3 Box. Its having problems shifting as the torque from the v6 is moving the motor around in the standard mounts. 

When driving normally, no problems at all. but if i am driving hard it becomes difficult to find gears

+1 for the MT-90, I have been using it in my SW20 for over 10 years and I have always had smooth shifts, even my TRD lsd did not need additive to stop chatter as the redline has it in its formulation

Yea the front engine mount was rooted but now its sikaflexed so its all good lol it has made a difference. 

Shaz, I've been speaking to Nik and when she says smurf blood she's referring to Superlight Shockproof not the Lightweight Shockproof as thats a GL-5 oil. I can't really find the GL rating for the Superlight Shockproof to be honest which is kind of strange. Although I have found that the MT90 is a GL-4 and is probably why some of the members in this thread are running it. 
 
Okay because of our stupidly large capacity I worked out pricing for 5 litres:
Superlight: $194.34
MT90: $175.60
Royal Purple Max Gear: $221.99

Might leave this here to get people's opinions now that cost is a factor haha.

Thanks for the info Matt.  Wow..... costs a bit more than I was expecting.  And probably an expensive job to replace the whole lot when having to pay someone to do it.  Might just have to put up with mine as is for a bit longer.

Yea quality comes at a price. Happily for you, you only need to purchase 4 litres. The install is actually really easy I have a pump so just let me know and I'll come around and do it for you or my mobile mechanic will charge $25 to replace fluid.

I just found a product data sheet with some information on the superlight shockproof gear oil as well and it sounds like the superlight shockproof may also be a GL-5 spec oil so on that information I would avoid all of the shockproof gear oil range and look at the MT90 gear oil range that redline sell as it is a GL-4 spec oil.
 
http://www.redlineoil.com/content/files/tech/Gear%20Oil%20Tech%20Info.pdf
 
http://www.redlineoil.com/content/files/tech/Man%20Trans%20Lubes%2010-13-1.pdf
 

Fantastic Info Nik, thanks so much for looking into that I tried many sources to find the GL rating. I'll probably end up getting the MT90 then.

From memory many moons ago the local redline rep said the shockproof oils aren't rated as such as they don't fit the standard oil testing regimes, or something like that.

If you don't have a clutch LSD you have lots of choice. Another option is ATF, some say that's mad but my mate ran it in his turbo for many years without issues.

There is also a fully synthetic Mobil oil that's quite good.

Current car has the normal castrol gl4 mineral oil. Works well, can be a bit notchy first few shifts when cold.

When filling you can use a bolt in the top of the gearbox, makes it quick and easy if you don't have the standard air box. Just need a funnel and hose. Undo the normal fill plug also so you can tell when you have filled enough.

Cheers

+1 for GL4
FWIW
I have used Amsoil GL4 75W/90 for several years now in my S54 box.
No probs whatsoever, with smooth shifting in all gears. Easy shifting when cold, as well as hot. 
http://www.syntheticwareh.se.com/synthetic_gl4.htm
 
For easy trans oil fill from underneath I use one of these suction pumps:
 http://www.ebay.com.au/it...UN-500cc-/191634169500

I've been using these, best I've found yet. Moves alot of fluid fast.