My L2D has gotten fussy and will not run in Turbo mode on my old Sanyo 2700mAh cells anymore. Same symptoms you've described. If you have some other cells, try them in there as a fact-finding step.

For the record, an L2D Q5 was measured at 145 lumens out-the-front on Turbo in an integrating sphere. 180 at the emitter, perhaps.