Actually all the 655 rev b1 router works well as the dir-825 as i have both. Lets offer to do some trouble shooting before we comdem that there is anything prematurely wong with any of these routers. Alot of problems can be placed in the configuration of routers or w ISP sevices.
Can you give us some info on the 825? Post over on the 825 forum. What hw version is it? What firware is curently loaded? If your having problem w the 625, please visit the 625 forum and will try and help you out for either product.
Im sure we can find a solution.