upon shifting from 3rd to 2nd for a slow hard left the whole bike lurched, didn't think I was moving to quick, what could cause this besides excessive revs or speed ?

What you describe is just the rear tire breaking loose (sliding) for a foot or so under the combined braking force of the drum brake and engine's compression braking. No big deal if done before you lean into the corner. Release the clutch IN the corner and break the rear tire loose, and the results can be disastrous. You’ll slide down, or start down, then suddenly get traction and “high-side.”  No fun either way it goes.