Heating issues with Masterbuilt 40

So from new my masterbuilt ran a little cooler that what the digital readout showed so I've always kept a thermometer in the exhaust vent. I fired it up today to smoke a brisket. I generally set it to 240 in order to get an actual temp of 225. Today 240 only gave me 190. I raised it to 250 and got 199. I'm set at 260 now and only seeing 205.
Each increase shows on the built in readout to be heating to the selected temp but using a dial type and digital meat thermometer is is not.
Anyone have this issue? Control panel issue?

Kmm said:

It might not be the smoker...two quick questions...
1) have you recently calibrated the thermometer you are using the exhaust vent?

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I have two Thermometers in the stack both have been calibrated.
Sort of. I know exactly what my hot water temp is, 123. I run about 2 mins of hot water in a large cup to with both setting in the cup. They read the same.

Kmm said:

2) was the ambient temperature significantly lower durning the cook?

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Ambient temp was quite a bit cooler. 54 degrees when I first put on the meat. This morning, 43.
The built in meat prob setting on the rack just above the brisket also matched the stack temp.
The stack temps this morning were fluctuating between 214-220. Meat probe was too until I stuck it in the brisket. Brisket seems done. 205 and soft as hot butter. The built in thermometer was showing 260.

mcyork28 said:

Maybe try running the temp probe all the way down the chimney to get a reading from the cook chamber?

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Yea, I think that brisket was keeping the heat down in the lower section.
I pulled it and stuck it on one side of my grill with a burner on the other side holding it at 200.
Put 3 racks of st Louis Style ribs on. within 15 mins all probes were reading 265-270 with it set at 260. :shocked:
I dropped the setting to 230 to see where it's going to level out. Will probably drop it some more. I don't want to open it and let more heat out but I may do so and move the meat probe to the rack under my ribs just so I have multiple reading locations.