What you've quoted me on in your post is not referring to a CRD Patrol, Bigrig (who I was referring to) has a GQ with a turbocharged 4.2 petrol engine.
It would not be essential to do a transmission upgrade on a chipped and exhausted CRD. For what you are planning you will only need a big transmission cooler, the rest of the transmission will be up to the job.
Tony