theres loads of threads on here about remapping a td5, Search Dynachip as most on here use him, i did too for better mpg and smooth effortless power esp when towing, the chap is proper nice bloke too, total enthusiast and knows his stuff.
Dont think too long about doing it, it cost me about £250, i raised my mpg to about the 30 mark but best of all is oooodles of grunt, It will pay you back in no time.
Just do it!!