If you have not done so yet, download Dolphin Browser HD. It's the absolute best browser for the EVO. Can view ALL web-sites like I am on my desktop. Just open up the Dolphin browser>menu>more>settings>User Agent and change to Desktop. Works flawlessly
I don't think anyone ever said flash would be ultra smooth on the EVO. If you look at most videos samples with flash 10.1 running on android, they are not super smooth. Flash in general will bog down browsing even sometimes on regular PC.
I still remember when I had the Moment, we were all eagerly anticipating the coming of flash to our phones with 2.1 on the horizon... then struck down violently as we were told our phones processor couldn't handle it. NOW, with a superphone that actually runs it acceptably, people like OP cry about it not being super fluid and flawless.
I can say, yes, it would be nice if it ran as smooth as it does on my computer, but we're not QUITE there yet. For now, just enjoy it as it is, and realize that you have actual full flash running in your phone, allowing you to do things other people can only wish to do on their devices.
I hate having to resort to that, but its about the best I can tell you, guy.