If the exhaust is too hot, suggest the possibility of the fuel not being completely burned in the engine. With new cats, the combustion will continue - so perhaps look for a cherry red cat as a sign.
As mentioned above - if the spark is too late in the combustion cycle, the fuel will continue to burn as it leaves, also bringing up the chance of burning the valves, so check the timing.
Recommend to pull the codes to see if there's a problem with the O2 sensors - looking for a 'too rich' type fault.
May not hurt to toss in a can of fuel system cleaner such as SeaFoam to ensure the injectors are misting properly.