NO and NO2 emissions are within compliance for Southern CA regulation purposes. You won't be de-foresting as you heat your bath water.

Are you restricted to electric and at what electric service size max or is nat gas on site?

"I get this behavior on all hot water lines. What floater or heat expansion are you talking about?" By "floater" I mean something that's suspended in the HW tank and is drawn toward the outlet when the water flows. The water would flow freely at first but when this obstruction is drawn to the outlet it would diminish. By "heat expansion" I mean some portion of the outflow plumbing that expands as the hot water begins flowing through it thereby coming to restrict the flow as it enlarges. From your description, I'm suspecting something involving one of the other of these is at work. Since you say the behavior didn't happen until the new tank went in, I'm thinking whatever it is must be associated with that new install. Like Chris Davis, I, too, would be interested in learning whether or not you also get low-flow on the cold water lines when this happens with your hot-water lines. That would tell you a lot. From the time you turn on the hot water, how long does it take for the flow to diminish? Is it about the same amount of time each time? If you then turn it off for a minute or so and turn it back on, is it still diminished or is full flow back again? This is interesting.

Make absolutely sure you don't have a closed plumbing system If you do then correct for thermal expansion. If you have hard water or water with a low or high PH correct those problems. Drain the WH once a year without fail. EZ to forget to do, but if you don't forget it will pay off in the long run.