Clutch shoes gradually wear out over time. Someone inexperienced with nitro RC might not know when it's time to replace them for the first time. The wear can be so little that it can be impossible to visually see when they need to be replaced. 2 gallons is quite a bit of run time for one set with my experience, although that depends on what car you have and the materials used. The people at your track might be noticing that your engine is reving high and not going anywhere fast. It will seem like your car has a slipper clutch that is set too loose (clutch shoes basically are the slipper clutch for nitro).
Go buy new clutch shoes.
Best case- on the first run with your new shoes, you will notice the difference for yourself and be able to tell when they need to be replaced the next time around. First hand experience is much better than the best answers you will get online.
Worst case- nothing changes. You now have a new set of clutch shoes, and judging by the current wear, you will never need to buy them ever again, although this is unlikely.
