Welcome and thanks for all the details of your situation. It makes answering much easier 🙂
Would the wide board be causing me to put too much pressure on my lead foot trying to turn?
I would not be surprised if that was the source of your problem. With a size 10 boot, there is just no real reason to ride a “wide” board. It will just place undue stress on your feet and ankles (which may be contributing to your heel lift) and increase overall fatigue.Plain and simple, get a normal width board. It may be OK to go with a SLIGHTLY wider board due to your higher weight, but not being a tall guy, you really cannot leverage that weight as dynamically, so don't go more than say 25.5cm wide.As for length, not too important unless you are having problems floating in powder. Otherwise, the 159cm length should be fine. 😎 Ride