Since the transmission is adaptive, I suggest you pound the throttle more often to get it in its aggressive setting, or stick with Sport mode. For some reason, X5s tend to upshift early unless you really pound it. Everytime I hear an X5 accelerate it upshifts the second after it gets going....

(X3 is totally opposite; tends to upshift too late and holds gears far too long on small uphills unless you get the fix)