About Endurance?

I am sometimes faced with the challenging task of playing Mahler's works without an assistant, my question to all of those out there who happened to need to do the same on a regular basis while in the orchestra would be, do you leave something out? is it possible to play trough the entire thing without having to get the horn off and put it back on again to be able to get to the end? I warm up to my best every morning before rehearseal but sometimes I feel that as I much as I try to play let's say mahler 5, everything on the part, I get so tired at some point that I just seem not to be able to go on any further......... any thoughts?