Gas stove with too little oomph

The other day we preheated the oven to 425, at 380 we put in two casseroles. Half an hour later it was at 385. Flame seems small. It appears to have a non adjustable main pressure regulator. It has a filament for the oven and then the gas turns on from its own relay down there, I guess. Is there a chance that the valve down at the oven just isn’t opening wide enough, flames seem small, maybe 1/4 inch

Digital or a knob?

Digital. 

That’s what I take to be the valve/relay

Here’s the main pressure regulator. It’s not adjustable there’s a plastic post in there, you put it one way for natural gas, the other way for LP

Heres what it looks like inside

The range seems to burn okay, I’ve never had a gas stove before so I can’t say for sure. Stuff cooks, at least. Although some are pretty bad

Ya know, it has a sticker that it was once converted to propane, although apparently at least somewhat converted back; the regulator is on NG and that oven relay thing has “NAT” in its name, so I assume it’s fine??

FWIW it’s model MGR4451BDB

Is it possible it is just controlling to a lower temp?  Like it's reading off by 40°F maybe try setting it to 465 and see if it hits 425.

As soon as I pulled the casseroles it proceeded up to 425 (slowly— its always been super slow)

I don't know where the orifice is on a gas stove but any chance the wrong one is in there or it's clogged with debris?

comparison of gas vs propane orifice for a gas grill; gas is larger:

City gas, I presume?  Any other gas appliances in the house?

I'd say faulty regulator / inadequate supply. 

You could always rig a blower and  a bottled oxygen feed. 

No, that was a joke.  Don't do that.

Thanks for the comparison picture. There are five orifices (orificii?) so I guess I’ll pull all and just look and clean at the same time. Dunno about pressure at this appliance or anything. Our gas furnace and water heater work fine so in general the supply seems good. 

And LOL about the oxygen and a fan. I have played with MANY oxy-acetylene balloons. I KNOW the value of a little bit of O. 

The fact that it has been swapped twice makes me suspicious that some part is incorrect.