I do a number of regular trips up and down the motorway and usually get around 38mpg rising to just over 40 on a longer trip if I'm not pushing it too hard. This has been very repeatable over the car's 2 year history with me, especially for some of the regular routes, which I do over and over. In the last couple of months that average has worsened and now I get 35mpg at best, 33mpg yesterday. The car runs without obvious issue, maybe down on power. It's just been serviced by APS and there was nothing reported. I'm thinking of getting it on a rolling road and having someone analyse the exhaust gases, any other suggestions as to possible causes or investigative techniques?