Have you installed any new apps by chance? Also have you looked at what is running? Menu>settings>applications>running services. Task killers wont always kill everything and kill somethings that shouldn't be sometimes. Another thing to try is watchdog lite in the market, its free and it will alert you if you have a rouge app.

 

I recomend SystemPannel to see what speed your processor is running, and how how much load it has on it. I have found an app or two that were just killing my processor when they had issues. I was able to remove them and re-install them and that fixed the problems.

 

Watchdog is also a good app to see whats your CPU up to.

 

Are you experiencing auto rotate slowness? If so, try recalibrating your phone using the "horizontal calibration" setting but place your phone with the screen facing downward with part of the screen off the edge of a table so you can click the calibration button. I did this and my phone works like normal again. I found the Froyo update to be very buggy!

 

Try the EC05 Stock Plus ROM - it's very fast, and it got rid of the carrier bloat.

Also, be careful of how you use app killers. In Froyo, app killers may do more harm than good. Froyo takes care of apps very well. Some app killers actually cause Froyo to run slower because it's working against the efficient nature of Froyo.