Drops out at high load

Hey All, I am new to this forum, but look forward being a part of it! I have a 2003 Polaris XC 600 with the liberty twin and the flat slide carbs. When i bought it in 2009 it had a top end bog that i didn't know how to deal with so i brought it to the local guy I use. He said the reed petals were bad on the factory intake reeds. He replaced them with some composite aftermarket reed petals and the sled ran great for several years after. Fast forward to the last two years and the top end bog slowly started repeating itself. What i mean by that is that it bogs out under load (deep snow). On the flat trail you can feather the throttle and get it past the hump. I tried buying some used (good shape) stock reed valves from a local used parts dealer and that actually helped, but not all the way. Last year i ended up buying some Boyesen dual stage reeds and tried those. The problem got way worse. I have worked on sleds my whole life but admit that carburetors are not my thing...hence why i am here. I did take apart and clean the exhaust valves and confirmed they are working properly. I also rebuilt both clutches thinking that could be the problem...to no avail. Everything on the sled is in top condition except this issue. So i have to believe it is a carb/intake reed issue. The instructions on the Boyeson reed package says that the reeds could make the main jet run rich and the pilot jet run lean. I am guessing i need to change jets, but have never done that before and am not sure what jets to buy. I am certain i could get the carbs out, i know where the jets are, but no idea how to change them or again...what size to buy.

Any advice would be appreciated!

Thanks!

Drops out at high load