01 Recon, no power in top gears

Hey guys, I have a very old and abused 2001 Honda Recon (non- ES model) that I recently put back not the trail after sitting for a long time. I replaced the rear axle that had stripped splines at the end from riding it with a loose axle nut, rebuild the carb, adjusted the valves and a few other things. She starts up and revs right up now

Anyway, the bike has plenty of power in 1st and 2nd (at least for a very high mile bike) but when you start to shift into third or higher, it starts to run out of steam. It doesn’t feel like power loss to me, there isn’t any misfiring or breaking up in the engine. it feels more like there is some slop in the driveline causing some slip of some sort. It’s hard to explain, but it doesn’t feel like the driveline is fully ‘connected’ to the engine and there is some chattery feeling when at the bottoms of the gear. The engine isnt free revving, but the bike just wants to lug along and struggle to pick up speed, even on flat ground. The more throttle you give it, the more it feels like your lugging it in too low of a gear and the chattering feeling gets worse. If you manage to make it to the top of the gear, it feels bit better but it’s hard to even get it there unless I’m on a flat street with very little load on the motor.

I’m not too familiar with the clutch assemblies on these ATVs but I am figuring I am going to have to learn. What do you guys suspect? I thought maybe the engine really is just down on power from many years of abuse, but first gear feels like it could still pull a truck, second revs through fine and the chattering feeling makes me feel like something else is going on other than it just lugging from lack of power. I think I remember this problem starting when I used to take it out on snowy roads where I was constantly shifting up through gears spinning but not really going anywhere, bogging down and what not. I think I abused the clutch pretty bad there. What do you think I will need to fix it?