BMW M51 diesel, moderate tuning

[Jomac]

I've been reading up on various tweaks that can be done with the BMW M51 engine and it all looks exciting if you have a bottomless pocket and can afford to do these things. I have a P38 Range Rover 2.5 which has the performance of a docile slug.! There is a performance tuning box fitted and it makes only a very slight difference to the overall performance. Are there any other basic tweaks that can be done, preferably DIY and tweaks that wont break the bank?