Well first off, i'll give you a warning. I don't know just how much practicing "hardcore" means, but overdoing it can be worse than not doing at all. I'm not talking about your chops, I'm talking about the health of your hands. Make sure you don't overdo it.
Any way now on to other things
As for why things aren't changing, i have no idea. However there are some simple things you can do to help your playing drastically. (or at least in my experience.)
- A good warmup program is essential. You mentioned that you play basics to start off, this is good so don't change that. However, the difference between the warmup you have now and the warmup you played in the drumline back during marching season is the level of focus. Make sure you have as much if not more focus now than you did back during marching season.
- Keep your level of focus throughout the practice session.
- Put a lot of emphasis on basics. I'm not saying that this has to be your whole session, but a solid foundation of fundamentals is essential. ( You have to walk before you can run)
- Take breaks from time to time. Not every five minutes, but if you go too long without a break, you lose focus.
- "If you aint havin fun, you're doin it wrong!" (scojo)
- Learn and keep your rudiments up
hope this helps