If you have been using that dose consistently, for that long, I am not surprised that you no longer derive any kind of energetic euphoria from it. I don't think it's the type of opiate you use: oxycodone is widely noted for being the best "upper" of the opiate family.
I have a suggestion, which you can obviously take or leave. Have you considered taking a planned "withdrawal break" in order to reduce your tolerance? Back in my heyday, about three days abstinence was all it would ever take to reduce my tolerance enough to make me feel like a novice the next time I took anything. (Mine were never planned, btw, but were when I'd run out and be forced to white-knuckle it till I could obtain some more.)
Those three or so days will be nasty, but I think you might find that the time you put in being uncomfortable will prove to have been worth it. I used to get a hold of some benzos and pretty much sleep the time away. The first time using after that would be sheer bliss, like it was the first time I ever used. Tolerance goes back up very quickly, but this will work for you at least short-term, especially if you restart at a lower dosage than you are used to. (Which you should defininitely do for safety's sake, anyway.)