I am currently playing a 2-1/2 Rico Royal on a Yamaha 4C mouthpiece. The reed starts out fine with what feels like the right amount of resistence. Then after playing a while it starts to get soft and then the high notes don't pop out well and I have to go to the next reed in the rotation. I have tried #3 RR but they are just too stiff. I wish there was a 2-3/4 but there isn't so I ordered a legere #2 reed hoping it won't go soft.

Maybe you should try a reed cutter and then cut the reed so it's the right size... I think I would do that

Try Vandoren reeds. They are about a half-size thicker than their Rico counterparts, so they might give you the extra strength you need.

Take vandoren as the one before said.
they are the best... RIco is really bad and awful.
Take Vandoren's 3 reeds, you will see the difference.

You're problem I think is that you're mouth muscles are strong and the 2.5 do not resist... so take vandoren and a higher number. If it's to easy to, go to 3.5