Sorry for the long post here but I just got through trying to fix the same issue with my sled and hope that you find the answer to your sled problems here.
This sounds exactly like the same issue that I was having on mine. I posted the similar thread about 2 weeks ago trying to get some answers. My sled is a 2016 Axys and I have the BD base sidekick kit. We ride between 8500 -10k feet. What is your set up?
It ran awesome all last season and then at the beginning of this season it started doing what you're talking about. I also swapped plugs up on the mtn. and it ran great for a minute or two but then went back to what it was doing before. It took me about a month to figure out what was going on and finally just yesterday I got it figured out. In regards to the Det issue... I had to mix 1-2 gallons of race fuel last year to get it to not Detonate. I was mixing Sunoco 100 octane unleaded race fuel last year.
Below is list of what I did in chronological order.
1. Started out mixing Sunoco 110 octane leaded race fuel this season. Did this because it was the same price as the 100 octane unleaded fuel and figured I could achieve the same overall octane with less race fuel and ultimately less cost. I'm not 100% sure if the 110 race fuel that I bought was bad fuel or not but decided not to use it. The major bog problem continued.
2. Checked the primary spring, cam arms, rollers, and spider and found no issues. Put about 5-6 ounces of Seafoam in about 5 gallons of 91 non ethonal fuel and ran the sled and it actually ran pretty good so I thought I had found the fix. On the next ride it was right back to bogging.
3. Swapped my secondary clutch with a team tied clutch and the bogging still persisted. I felt confident that it didn't have anything to do with clutching at that point.
4. Plugged in my brothers E-Key from his BD kit and also moved the T-Map sensor to several different locations but the bogging was the same.
5. Checked all rubber boots to make sure there were no leaks and also checked all electrocal connections. Especially checked the relay switches that have the connection that goes to the exhaust valve servo coming out of them and applied dielectric grease to them. Still the same Bog
6. Found the thread on here about the coolant line that runs off the coolant bottle and to the front of the motor and how it rubs on a bolt and can rub a hole through it. Checked mine and it was almost rubbed completely through. I zip tied it up and out of the way and covered the tube just to make sure it didn't wear any more. I also decided to do a compression test and each cylinder had about 110 PSI which, according to Jared Sessions, is good given my elevation that I tested them at (about 5k feet).
7. Cleaned my own exhaust valves. The dealer told me that he would have to clean these as it takes a special tool and it's quite a process but he was 2 weeks out from being able to get to it so I choose to clean them myself. When I tried to pull them out they were so gummed up that it was very difficult to get them out (my sled has about 550 miles). Spent about 2 hours just cleaning them and put it all back together and figured that must have been the problem but the bogging continued.
8. Took it into the dealer to get the exhaust valve calibrated and have him do a diagnostic test. He said there were several codes showing that the exhaust valves had been removed and hadn't be re calibrated but no other codes. He did the re calibration and I took it up and NO MORE bog. BUT...... My sled would only hit about 7800-8000 rpm. I was definitely happy that the major bogging was gone and do feel like the exhaust valves were the issue with this but I still needed to figure out why I wasn't getting the RPM that I needed.
9. Took connections off of turbo itself(exhaust/muffler, Charge tube, and air tube) to check impellers and they looked fine. Also pulled the aluminum air box as BD said that some of the early boxes were breaking at the weld on the outer edge. I plugged all the holes in the air box except one and shinned a light inside(I was in a dark room) and couldn't see any light coming through any breaks or cracks. Took the mid pipe out and and applied high temp silicon to the connections on both ends and when I took the muffler off the turbo it nearly fell apart. Most of the rivets on the canister part were pulled through and it was about to come into 2 different pieces. I called BD and they sent a new one(remember that this is the 2016 kit so it doesn't have the updated better exhaust that the 2017 kits have). Clamped the new one on and went out for ride to test it out in 2+ feet of fresh powder and it ran just like it did last year. No bogging and I was getting the RPMs that I wanted. I was so pumped to finally have my sled back and ripping after month of trouble shooting and not being able to actually ride.
My conclusion is that the exhaust valves need to be taken out and cleaned at least every 500 miles or before each season and they need to be re calibrated once they go back in. Make sure the exhaust connections are good and tight as they can be. Make sure your muffler isn't coming apart.
With regards to detonation.... Me and 3 buddies have these turbo set ups(all on 2016 axys') and have found (given our elevation that we ride at; 8500-10k feet) that we need a total octane of somewhere between 92-93 in order to not throw the Det code and feel like non ethanol fuel is the way to go if you can get it.
I hope this helps you figure out your issues!!
