yeah i've got the instruction book on pdf too
nistune is the best option but not available for r33's yet
power fc is the most common aftermarket but exxy at $1k+ used
if your just chasing a bit more power and better economy then this should do the trick, seemed to help in my 32
also, your probably best to replace your o2 sensor if its a bit sluggish in the lower rev range, www.kudosmotorsport.com about $77 if you go pick it up from nerang (i think)