I think its way too early to tell if its a mistake to upgrade or not. If certain things like sling are a deal breaker, that's personal preference and so be it. Overall coming from the tp2, it's going to be a transition. There are some things I've noticed that don't work for me on the evo and work on the tp2. The are also things that the evo does much better, web browsing for one (even in 3g) is much faster for me. I haven't had the time to research them to determine if there is an app that will change that. I'm betting/hoping there is.
For one, need to find a coreplayer type player for android. Anyway, the tp2 is a great device as well and I personally would be happy with either one.