Hey all, question for you dtukers. I'm starting a new job and moving from being home based with occasional travel to commuting 450 motorway miles a week.
I've flirted with getting a dtuk for a long time and I'm thinking of getting one shortly. I know the dtuk can give comparable mpg maybe even improve it in some cases, but what about motorway miles?
At say a 75mph cruise, are we going to be more or less efficient??
I'm going from a 45p a mile job to paying for 20,000 commuting miles out of my own pocket - so it bears thinking about! 
It'll be about the same, although the MFD reading will be more optimistic with one one. It might be a smidge better. If your MFD (at stock) is currently reading around 3% optimistic, it'll become about 9% optimistic with the DTUK box on. If you were actually doing 45.0 mpg for a trip, the car would be reporting 46.4 (stock) or 49.0 (DTUK). The car is always using a little more fuel than it thinks it is, and so when you're using a "normal" amount of fuel, the car thinks it is being extremely frugal.
In the Summer I did a round trip from Newcastle to Leeds (105 miles each way), and got an actual 54mpg down and 58mpg on the way back (59 and 63mpg indicated) – maintaining 80mph, except for a 10 mile stretch on the way back through average speed camera zone – explaining the extra 4mpg I got going home.
I had far fewer active/forced regens with the DTUK box than I’m getting now (some of that may be due to winter driving, and the warming up inefficiencies that come with), my Dad now has mine on his DSG GTD and loving it. I gave mine up thinking that in winter on Bridgestones I really didn’t need the extra power (but miss it), and I’ll appreciate the R more (if it ever gets here) coming up 116ps instead of 60ps.
