So for the WOT issue I should focus on the high speed Jet? I believe it is accessible after the bowl is removed

 

Yes the main jet is the larger round jet. The pilot jet is recessed,takes a small screw driver to remove it.Several videos on youtube that can help. This guy went to a lot of trouble tearing things apart that wasn't necessary,but look at the 2:15 mark. Plus here's the fuel section pdf from the service manual on your BST34 carb that can help understand carbs better.https://www.google.com/url?sa=t&rct=...U2gGlaHJWSIlbA

 

I swapped the OEM Mikuni carburetor back on the trail boss last night. I checked the idle fuel mixture screw on the aftermarket carb and it was a full 3.5 turns out.
Having said that I backed off the OEM carb to about 3 turns out. Note: it was only 1 turn out when I removed the OEM carb.
Anyway, the OEM carb was idling better than before since the idle fuel/air mixture screw was opened up to 3 turns from 1 turn. At WOT it runs strong like it did before. No bogging or hesitation.
Comparing the OEM carb to the aftermarket carb I can make the following comparisons:
At cold start and idle the new carb works better. It's idle fuel/air mix scew was a full 3.5+ turns out. However at WOT it bogged badly.
At WOT the OEM carb is far better - no bogging/hesitation and runs very strong. I have to assume the aftermarket carb high speed jet is undersized.
I am guessing the difference in performance at cold start and idle has to do with the fact that the OEM carburetor should be thoroughly cleaned (both high speed and low speed jets with a new float needle and seat.)
I will keep the aftermarket carb as a back-up but will go to the Polaris dealer to buy the new bigger high speed jet and retrofit accordingly.

 

Or just swap the oem main jet over to the new carb and see if that solves it. Just compare sizes that are marked on the top. On the Mikuni carb cheaper just to get a new rebuild kit from Shindy that comes with all jets, needle and seat,jet needle,pilot screw,etc.

 

I removed the main jet from the aftermarket carb. When I took it to the local Polaris dealer, he noticed that the aftermarket main jet was actually way oversized to the OEM specified jet size for the Mikuni carb.
The main jet size on the aftermarket carb was even bigger than the #135 main jet at the dealer. I bought the OEM specified jet #122.5 (for 2003 Polaris Trail Boss 330 and several sizes down from the #135 jet) for the aftermarket carb.
Apparently at WOT, the aftermarket carb was providing too much gas (flooding) causing the engine to bog at WOT.

 

That's why I always recommended for people to take the Chinese carbs apart,clean and check jetting. I don't trust them and sounds like you confirmed it at least on this carb.Some people have even mentioned finding machine shavings and trash in these carbs and one person posted that one port wasn't machined all the way through. Hope you finally got the problem solved now.