Does any 1 have a tunit chip, on a range rover 2.5dse p38 1999. i was thinking of buying 1, and wondering if any 1 had any info on the tunit chip. how much does it improve the p38 dse on bhp and also fuel mpg. also where can i get 1 from by leeds and how much is it. what are the positives and negatives if any to this chip. thanks