The "det" issue 99% of the time is the motor not being loaded hard enough and over revving causing a false detonation code to be thrown on the computer. this can be solved by running heavier weights, adjustable weights are nice because they allow you to load the heel super heavy which is what this torquey big bore craves.
I'm having a hard time understanding your compression on your sled with the two different dome sets? All of the kits that we have done (8 in house so far) were 13.5:1 domes and all had between 146-149 psi compression running straight 91 pump gas at 2500-8k feet. Do you have a Rev 1 kit maybe? all of my testing has been done on 13's and 14's but we havent seen any cooling issues at all with the billet head, it will run 125-130 all day long which is right where the motor was designed to run.
The 858 kit has exceeded mine as well as my customers expectations, reliability has proven to be every bit if not more reliable than stock. When mapped and clutched right it is super torquey on the bottom end and in the mid range and the top end seems to pull and pull. 8500 rpm's has never sounded so good. I would highly recommend a 3" track to get that power to the snow though as it will spin the stock track and dig some pretty big trenches.
Have quite a few videos on my youtube channel from one of our shop build 858's last year
SPS YouTube Channel