I have noticed over the last few weeks that the response from the engine to the pressing of the accelerator seems to be delayed. I have also noticed when I take off in first gear there seems to be a rough sound like of a diesel engine of twenty years ago. Also if I was in slow moving city traffic it would be a little annoying. What I noticed this evening while driving home from work is that in 5th gear and at around 60 mph the revs were reaching 2500rpm, at this point the rev counter needle dropped down to 2000 RPM and you could feel the car slowing down slightly. I tried it a few time and got it to repeat I put the car to neutral and revved to the red line and there was no problems.Tried in 3rd,4th and 6th and could not repeat the rev drop. One thing I did notice was I revved it up and was up to 80 mph in 5th gear and the revs were at around 2500rpm. As engine revs should be the same as wheel revs for a given gear I was not expecting this difference. One other thing I noticed when the rev dropped it felt like the clutch was slipping or some thing else. Car is a 2008 Saloon 6 speed with around 109,000 miles on the clock. I have the car since 2009 and I have changed the oil,oil filter and air filter ( all Honda parts) last week and there has being no difference since I got these done. The diesel filter will be changed within the next 5000 miles. The MPG of the car is still the same at 47 to 49 MPG.