When I start her up first thing (cold) it takes a good rev for it to go into gear. 1st through to third seem to be the worst. It will often rev out before slamming into gear. I have noticed that when taking a hard right hand turn, it will always rev out before shifting. Any ideas on what the issue could be would be much appreciated! cheers.

trans fluid levels need to be topped up I would think. You probably would want to get the box serviced if your not aware of when it was last done. Or do it yourself. its pretty easy. there as tech links here that will step you through how to service the BTR, its just filter and fluid. providing you do it all correctly and there are no other issues with your box all will be good.