Rpms vs Speed

ok, I am ging to assume that your car is manual gear box.
The theory is here:
The engine block itself only burns fuel and turns. The gear box only provides different gear ratios when the engine provides it turning force, depending on the gear you choose. In between these two blocks, there is what we call CLUTCH. the clutch is a component that provides some SLIPPING between the Engine block and the gear box so that they can not engage 100% together, when the clutch is pressed. When the clutch is fully released, the engine and the gear box should be fully engaged, unless the clutch is fault and still acts as if it was pressed. This is due to wear on the clutch plate, or the springs that dont push the clutch hard enough against the engine, and the gear box. You can imagine the clutch is like a slipping plate/disc between the two.
at 7000km, I really doubt that your clutch has gone faulty. In my experience, clutch is the ONLY thing that can affect the speed of the car (in a given gear) when the engine is running at the same RPMs. IF it was your tuning issue, your engine should not be turning at those RMPs in the first place. If your engine has lost power due to tunning issues, then the car would move slower (due to lack of power) and also the RMPs would be lower when the car is in gear, as compared to a full power car.
I think everything is fine, and you havent observed it properly (unless you have managed to wear out the clutch within 7000km. I have a Nissan Primera 1600cc with OVER 200,000km still working on the original/genuine clutch from new.
Question is, does your clutch SLIP? do you know how to check that?
Let us know how you get on pls, and Good luck
AH.