On GXP cranks, the crank bolt is meant to tighten the LH crank up (bastid tight to keep it from undoing) on the spacer only (the spindle is 'stepped' for this) and the drive side is therefore floating (ie it doesn't 'preload' against anything). Sounds like you somehow have too much width across the total width of the bb shell/spacer/bb cups/little gxp insert, hence the drive side crank 'binding' against the drive side bearing.
I remember my gxp bb's only coming with 2 spacers for 68mm bb shell- I wonder if they are set up for the possibility of 73mm plus chaingide/e-type derailleur as shimano allows with 3 spacers? I would try removing the one spacer you ave and reassemble, see what the chainline and gap between the RH crank and bb cup/bearing looks like. (it should be very close indeed but as i mentioned ablove not actually pressed in against it). My, what a lot of brackets. Happy spannering.
oh, or your LH side bearing is seized, so little torque means the crank spins inside the sized inner race, and more torque means it fastens on to the spacer properly but seized bearing prevents it from spinning freely. If it still does this with no spacers then your bearings are seizing. (usually the left hand one first for some reason)
