Depending on where you're based, Van Aaken are pretty well known for improving diesels through chipping [they're in Crowthorne, Berkshire]

I think most places can tune them now

Also, Chip mentioned that Nitrous actually has some awesome results on diesels, he got technical and said something about propane and I got lost, maybe speak to him or a tuner you know that does it

AND WELCOME TO THE SITE