After taking a sort of Hiatus from bass playing, I've found my stamina to be pathetic. I have trouble even playing simply root lines without strain. I don't know if you guys would happen to know good stamina exercises for my fingers.
Run through scales, gradually up the tempo.
everywhere you go tap on stuff with your fingers. start out with soft taps. then after you build a bit of stamina go to hard taps. I do this and it helps me a ton. especially if i'm not playing bass for a while, since i won't lose my stamina inbetween spread out practices.
Bales recommended a book a while back that I will concur on, Bass Fitness by Josquin des Pres. Its great for building accuracy, flexibility and stamina.