I think even though you get used to it you should have a gut feeling that it's roughly the same as it always was. I kinda went through the same things recently but I knew it wasn't the engine, mine was a combination of my old clutch and me driving tamer.

The new clutch made my car feel faster than ever, then I got used to it too. It's never felt slower though, just less fast. Until I test the theory on an on ramp then realise it's still there.

If there's something wrong I hope you can find it and fix it.