M8 gearing question

The 11" secondary is like gearing down the DD but only on the bottom end. The top end speed or top end track speed shouldn't be affected by the larger secondary. The loss of speed when leaving the hardpack could be caused by a ton of different things but I would guess that the secondary spring you have is to stiff. When you lose track speed going in to the powder the secondary is backshifting really hard and essentially putting the sled in a lower gear. The STM is using torsion springs and I have had the best luck with the red and white. I would play with different secondary(helixes and springs) and primary configurations(both weight and spring) before you jump into regearing the DD. I'm sure you know but only make one clutch change at a time.