Arggg! 96' 250 Trail Boss carb issues, jet sizes?

96' trailboss 250. I am at the end with this machine, please help! I have gone through the carb repeatedly, all passages are clean. Checked timing, ETC, tank vents and oil pump function. Put a new top end on, bottom end still seemed tight and moved smoothly. Replaced fuel filter, fuel shutoff, air filter, spark plug. Exhaust pipe is clean. Adjusted needle settings to extremes and settled back on factory settings again. Some things have helped (some a lot) along the way but ultimately it does the same thing, boggs down after a short distance on the throttle. If you give it a few seconds to catch up it will often pick up again for a seemingly random amount of time, then bogg again. When it is making power it is great and throttle response is a lot better than when we first got it. But the bogging is just destroying the feeling of any progress or joy in riding it. I am leaning towards rejetting the carb at this point but not sure what size range to get in a kit for 60/40% - 4000/8000' in altitude (rocky mountains)? If you've got any info on jets or suggestions on other things to check - PLEASE! - Let me know.