Hi.

Have you checked your internal memory lately?
From your home screen:
menu > settings > SD & Phone Storage

Toward the bottom, take a look at the "Available space" under "Internal storage."
Is this number more or less than 50 MB?

The phone should still function decent on down to about 30MB, below that, you will definitely have some issues. Typically, I'd say keep it at least at 50, if not above.

If it looks like you are running low on space trying clearing some cache in some of your apps or removing apps you don't use.

If internal storage doesn't seem to be an issue, there are some other things to look at as well.

 

advanced task killer. download the apk and install it, then long press on the home screen and add a widget for ATK (advanced task killer) so that you can randomly just touch it as opposed to having to open the app all the time and doing it the long way

 

EVO 4G - Support and Troubleshooting: Sticky: Task Killers! Must read...

Perhaps try a task manager first so you can see if any particular app is taking over, and then kill only that app - or better, uninstall it.

Personally, I use Watchdog Lite (it's free in the market). You can see real time CPU and memory usage by each running service.