Power loss and fluttering noise in 2004 Prius

We are original owners of a 2004 Prius with 165K miles. We’ve taken excellent care of what has been a great family car. A couple of months ago, we got a check engine light associated with a catalytic converter error. We first replaced the oxygen sensor, which temporarily eliminated the error light, but the car really loses power, especially when a load is placed on it going up hill. The power loss is associated with a fluttering noise coming from within the engine and the battery display showing that it is not charging sufficiently. We took it back to the dealer and they replaced the exhaust manifold gasket and suggested we replace the catalytic converter (> $2000) but also recommended a local exhaust specialist who could replace the catalytic converter for much less. The exhaust shop examined the car and told us the catalytic converter was fine and did not need replacement. There are no more error codes, and the dealership and their service department has no idea what to do. Because the dealership shows no interest in repairing our car, we are looking for suggestions for competent Prius shop in central Washington state, or any other suggestions. Thanks!!!

You might look at Toyota based forums. I have seen toyotanation.com and it appears to actually have some members with real knowledge. Like all forums it also has people who don’t know any where near as much as they think they do.