In your opinion, what is the best way to gain endurance?

I actaully was about to ask that. I dont have a very high endurance. Im playing in a GR 12 band (i am Gr 11) I play first chair, and trumpets are always the lead.. I play ussually 3 hours a day Hitting high D above C.. I was wondering if you had any advice to give me on Endurance training. I also had another question, I use a 3F mouth peice and after playing i find that the mouthpeaice is Very hot... So ill switch to another, am i doing something wrong if i cant play becuase its hot?

First advice is to get rid of the cheater. I know I know maynard and all the other greats used them lol. But I use a 3c and i have a range capable of nailing primal scream on it. Don`t use them unless you have to they are meant for high register work only not for normal playing. Second I developed my endurance by joining the marching band and playing lead. If you are already doing that or can`t, do lots of lip slurs. Don`t kill yourself but do them until you feel tired, like after a good workout.

by the way the heat comes from constant pressure or just playing alot don`t worry about it but if its pressure back off a tad.