Re: Running rough at higher rpms when hot
I could be wrong, but in my experience when the cats are blocked the car feels like there's no power when accelerating, regardless of engine temperature. And you don't necessarily get a misfire, it just feel like the engine doesn't want to rev. If you don't trust what they're saying, you can remove the cats (when they're cold!) and look at the inside, you'll see if the ceramic honeycomb is broken or not, and if pieces of it are coming out when you shake it. Shake it in your hands, don't drop it, hit it or bang it against a hard surface because you WILL damage it. You can also drive your car without the cats and see if it feels the way it should, but it will be extremely loud and you could make your neighbors angry :) cheers
ps: If your plugs are burning out too quickly this is usually due to the engine running too lean (ie: blocked injectors, manifold leaks, etc) and causing the temp inside the combustion chamber to be too high. Investigate this issue, as it could also lead to cat failure.