cr250 1991 jetting question

Im sure this question is spread across all 2smokes, but I'm going to ask anyways :D

My bike runs great through most of the RPM range. With no load on it the bike sings a great tune all the way to the top of the RPM range. When I ride it though, it's a different story. I get great bottom end and mid range, although it does sputter up on the top end a little bit. Does this mean it's running lean or rich? I can usually go on 2-3 rides (about 3-4 hours a piece) without having to swap plugs. The plug, when fouled, is not wet, but black. I'm assuming that's because I run a 40:1 mix of Redline and 93octane. When I purchased the bike I was told it was jetted for a higher altitude than here in TN (I believe I was told by the seller that it was jetted for riding out in Montana?). I purchased a 5 different jet sizes today just for the heck of it. I purchased them from the stock size (168?) to 175. Might I have more luck with the powerband after readjusting? I'm not a n00b with mechanics, just with 2smokes. I''m thinking I might have a cracked reed because it's not a consistent problem, although I just dont feel like it's got the balls under it that it should. Any feedback will be appreciated :D

I'll run a compression test tonight to see what I get. I was told the bike had a new top end on it when I purchased it. With a new plug in it and the bike being cold, I can start it on the 1st to 2nd kick everytime. That leads me to believe the top end is fine and that its a fuel issue that I'm chasing. Carb has been completely torn down and flushed with carb cleaner and compressed air.