I play the Trombone. How can I build up endurance in my chops?

Sometimes after a certain period of time my lips get very very tired to where I can't play at my maximum volume and it happens after running through a song back to back. How can I get my chops stronger so I dont worry about my lips and facial muscles hurting and air leaking out my sides of my lips. Because we do something that you would call crankin (playing very very very loud -__-) Like what Jackson State (A HBCU College) Or Southern University (HBCU in Louisiana) Any ways of getting my chops strong enough over time to build endurance. Other than Lip Slurs and Longtones because they get very boring so if any professional musicians or something got some tips please tell me and if you do how many minutes a day should I do it?