6'3 and 170lbs is not that abnormal. You are fairly skinny, but not at all too skinny. Plus we have to keep in mind that people usually aren't as tall as they say. My belief of being 5'11 was crushed with one visit to the Dr's office lol. I'm 5'9 :P
Anyway, my rant aside, you really have no need to be on a 164. The reason that board fit you is because it has the waist width of at least a mid-wide. I'm going to suggest you hop on a shorter board in a wide version. You are looking in the range of:
155-161 wide. Make note of some models such as the Lib Tech T.Rice. It doesn't state that it's a wide board, but if you look at the measurements, the 161.5 and up are wide models. Also, the Skunk Ape is the wide version of the TRS.
Here are my suggestions for boards that fit your style of riding:
Never Summer Heritage X 156 for more playfulness or 158 for more bomb proof stability
K2 Turbo Dream 157w or 160w - My review here:
Ride Highlife 159w - Very similar to the Turbo Dream, but a good deal stiffer. Instead of being flat in the middle, it is nearly flat. Has more pop as well.
Lib Tech T.Rice 161.5 - Sick big mountain board with C2 camber. Rocker between the feet and camber underfoot. Stiff and stable. Magnetraction is going to help with edge hold on ice/hardpack/crud.