Infiniti QX 56 2005 car. After running at highway speeds it won't accelerate without bogging out with severe loss of power. Have replaced plugs, coils, cleaned MAF, CLEANED OUT CATS. Only code showing is P0420, but that's because of the cats being cleaned out. Any other suggestions such as tps etc. HELP!

Alternator going bad could be the problem. I've seen it before. Severe hesitation because poor and inconsistent power is being generated so the coils don't fire consistently and no spark ignites the fuel. The fuel gets exhausted and saturates the cats and then finally ignites in the cats as an explosive backfire. P0420 typically means that a converter has worn out or degraded—not obstructed or clogged. But if the case is the latter, it can lead to engine performance problems, such as a lack of power, rough idling, and stalling, which are some of the common signs of a clogged catalytic converter. The backfire issue would concern me more because that can totally destroy the metal catalyst inside the catalytic converters. The alternator is relatively cheap and easy to test and replace.