Cutting out under load Sportsman 500

Hello all,
Sportsman 500, 2500 miles.
I have a problem with my Sportsman 500. I change out the start because it would turn over once or twice and spin out. after doing this the starter still does the same thing but there are also other problems that have arisen.
When I backed it out of the garage I noticed right away that it cuts out under load. idles and runs fine, but if I give it significant amount of throttle it cuts out and misses until I let off.
I pulled the carb and cleaned it out thinking it might be fuel related. after doing this it ran fine, I took it about a mile down the road and it started doing it again, a little at first but worse as I rode.
Through out this process I have put on quite a few miles and am on my second tank of gas, I also put sea foam in it before the last test drive.
The starter still spins out, but sometimes it also just makes a humming noise instead of turning it over. I am guessing the Bendix might be bad?
any thoughts on why it would be cutting out that way? anything I could have done changing the starter that would make it cut out?
I appreciate your input on this matter as its making me nuts.. seems to get worse the more I work on it.