ktdave,
the pressure and flow of your natural gas is dependent on a few things, and how those things add up will determine if you're reaching the the minimum requirement of your burner (heater.)
some of the varialbles are 1) what regulator in front of meter happens to be set at; all regulators have output "ranges", and yours may be set "high enough" to get enough pressure (or may not, if you're having problems). Also regulators have small orifices and can clog easily... so keep this in mind if you begin to have problems.
2) pipe size... the larger the pipe size, the more flow you will get, so if you're getting the full 250 cfh, that may be enough to operate your heater
3)length of pipe run... the longer the run, the larger your pipe size needs to be
remember, there are 2 factors... pressure AND flow. The mastertemp400 needs 400 cfh (flow) and somewhere between 4 and 11 inches of water column (pressure) (if I recall correctly from the manual.)
If I were you, I'd go ahead and change the meter. I doubt your gas company will charge you anything, and you're risking starving your heater without it. The results might show up down the road.
FWIW, I ran a large line, but I had a long run. 2" line for about 100', only used the regulator in front of the meter to drop it down. (your gas line probably comes in at about 2 psi, and needs to be dropped to ~1/3 psi) Probably not the least expensive option, but that's what I did. There are certainly other solutions.
I'll be glad to help if needed. (this is pretty much what I do all day long, but usually in industrial applications)
enjoy...