"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.

The following was posted by Lazypup on a similar question: Both the ASTM (American Society of Testing & Materials) standards and the plumbing codes require that the sensing probe must be in the upper 6" of the water heater pressure vessel. Typically they are side mounted on gas water heaters while they are commonly top mounted on electric water heaters. Either position is fine providing the T&P valve sensing probe is extending into the upper 6" of the internal pressure vessel. Years ago water heaters did not have Temperature & Pressure Relief Valves. Instead they had "Pressure Blowout Plugs" which look like the freeze plugs in an automobile engine block. When T&P valves first became available water heaters only had two threaded ports, hot & Cold, so they would install a close nipple and Tee on the Hot water discharge line and place the T&P on the top of the TEE with a long probe that extended through the TEE and nipple and into the upper part of the tank. If your old water heater has a third threaded tap on the pressure vessl where the probe is extended directly into the water in the tank you may use a standard T&P valve. If the T&P is on top of a tee you must use an extended probe type valve. If you need an extended reach type look for a Watts 100XL. The XL on the model number identifies it as an extended length probe.

skyclad- Let me again point out that a Pressure Reduction Valve (PRV) should not be buried and the city telling you that lines would have to be dug up sounds entirely bogus. PRV's do not last forever because they have an internal diaphragm that needs to be refurbished periodically (typically every 10 years or so). There is also an adjustment screw that you have to set to get the correct pressure, and sometimes you need to reset it if the supply pressure changes significantly. I'm not saying it's impossible that someone buried it -- in the concrete or behind some sheetrock -- but only an imbecile would do so. You may have a PRV somewhere and just be unaware of it. Or there might not be one, and you will need to have one installed. Finally, when the employee told you 130 PSI was "normal," all that means is that could be the normal supply pressure, not that it would be ok to have that pressure inside the house. Regardless of whether it's 150, or 130 or even 100 psi, as Jake said, you've got to get it adjusted down to no more than 80 psi.

Since this is just specific faucets, the problem is what Kudzu said. There is sediment that was stirred up when the heater was replaced and it has clogged the aerators. A good plumber will anticipate this problem and run the hot water out through a tub faucet or washing machine hose until that's flushed out. Then they will run the other faucets and clean out any crud that makes it to the aerators rather than walking away and leaving it to the home owner. The problem isn't "burping the water heater" (an explanation since retracted by Stax). That explanation was absurd. Sure there can be air in the top of the water heater and that will collect at the top and will exit through the hot water line as spitting and sputtering. Significant sputtering is a good thing to avoid, if you can, because it can cause grit to come loose and clog the aerators. Air will work its way out very quickly though - so "air" isn't the issue - crud in the faucets is the issue.