Yes. That is the correct stuff.  Fill with that and drive it for a few hundred km.  Take note whether the gear shifting improves.  IF it does I will then recommend another GL4 oil for you to try.
I have managed to save two gearboxes that had been playing up after using bloody GL5 oil.  Ive had several more that did NOT improve and had to be stripped and reconditioned.
Pay close attention to the clutch to check that it is fully disengaging as it can cause a lot of harm to the syncros.
You can PM me if you need to know how to check the clutch operation.

Thanks so much guys.
 
I've only driven it for barely anything right after the oil change, it's still pretty ****ty. Rev matching in neutral is fine though, like butter.
 
Falcon I'll PM you, I'm a bit of a noob.
 
Reddtarga, I read bits of that article before, it's pretty interesting. Thank you for mentioning it anyway.

Or you could just leave the ATF in there.

So many views on oils, you have quite a few choices.

Cheers

UPDATE:
Been driving for about 500kms+ now on ATF DEXRON III as recommended by Falcon.
Downshifting into 3rd is much better, it's SLIGHTLY notchy, but bearable in most cases indeed.
 
I'm having issues upshifting into 2nd though. When I rev past 4000rpm or so, and try get into second, it's very tough to get into. If I rev out all the way to 6/7000rpm and try powershift to 2nd, forget it, it WILL GRIND.
YES, I am depressing the clutch fully.
YES, I am keeping it depressed till I shift into 2nd, then letting go of said clutch.
 
I tried WAITING (although I shouldn't have to) for the revs to fall into the right spot for 2nd gear, but it STILL struggles to engage without minor grinds and notchiness, it will only engage till revs are 1.5k rpm ish where 2nd gear WOULD be at said speed. Of course that means when I let the clutch out by that point, then the engine will have to compensate for the low revs and bump it up to whatever will match the road speed on 2nd gear. *sigh*
 
It's just stupid.
 
I don't know what to do, might have to get a different gearbox. I'll finish up this tank of fuel and hit 1,000kms and see how I go.
 
Big thanks to Falcon!

xez
You probably just need to replace the synchros, maybe only just 2nd and 3rd. Should be cheaper than replacing the whole gearbox...

I'd disagree on that... you can pick up good condition S54 boxes for under $400, even if you were to rebuild it yourself, you would spend well over that price. Just my 2cents worth.

So here's another update.
The S54 has been leaking, and it's very possible it's the seals for the output shafts.
I've totally sealed the bottom drain plug for the gearbox fluid, I thought it was the cause because it appeared to be weeping, but upon further inspection, I noticed the leak is likely to have been coming from up top (the output shaft), or both even. Anyhow.
 
I'm not 100% sure on the part #, and I'm not 100% sure on the process used.
 
Can anyone direct me to a guide that is fairly accurate for the MR2.
 
I was told to replace the output shaft seal (picture of leak/problem area attached), and from looking around, I've found 2 different things that I can buy, but I need to confirm the part #s first.
 
The 31115A looks like the correct seal, can anyone confirm?
 
Thanks for your help so far everyone.
 
Pictures: http://imgur.com/a/DpGTl
 

Awesome.
Thanks Mister2.
 
I made the right call and ordered the 31115A, but only one, as the right side was dry as a bone.
 
I already made the order through Toyota for $16, it's worth it considering I am picking it up tomorrow morning!
 
Thanks once again for confirming this.
I'll let you all know how it goes.