I finally received a response from Traeger a short while ago. This is what they said. Tell me what you'd think of this response:
Thank you for reaching out the Traeger Support team. We're sorry for the late response.
We're sorry to hear about your grill's temperature fluctuation. We apologize for the inconvenience that this issue had caused you. We'd like you to try the following steps to help fix the issue of your grill.
Traeger Grills are going to fluctuation in temperature. This is completely normal. It occurs in your electric home ovens, and will occur on your grill.
What should you expect your temperature fluctuations to be? On average, over at least a one hour cook, in nice weather, your fluctuations should be no more than +/- 25 degrees.
If proper expectations are established. and grill is outside performance parameters, follow troubleshooting steps.
1. Ensure proper startup.
2. Ensure Shutdown was done properly, if both are good, continue to next steps.
3. Check pellet quality.
4. Clean grill (Especially fire pot).
5. Check the ambient temperature when starting the grill and make sure it is within +/- 10 degrees.
6. Check the grill components to make sure they are in good condition (Fan, Auger Motor)
7. Check internal integrity (drip tray, fire pot, heat baffle).
7.1. No holes form rusting through, some warping is okay and will at most create a small hot spot.
8. Repeated Opening and closing of the lid too often can cause temperature issue.
If the above troubleshooting steps don't fix the issue, please do not hesitate to contact us again at 1-800-TRAEGER and we'll see next available options for you.
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Here's what I originally sent them along with the pics from replies 21 & 22 in this thread:
I have a new Pro 575 that I purchased earlier this week. I'm finding that after a couple cooks and test sessions the temperatures the grill thinks it is at and the actual temperatures are way off when at higher temperature settings. At lower temperatures, this issue does not exist. What I am finding:
At Traeger pit/controller read temp of 250, actual is 225-250
At Traeger pit/controller read temp of 350, actual is 285-300
At Traeger pit/controller read temp of 450, actual is 350-370
After finding that it took 90 minutes to cook a package of bacon and some burgers at 400-450 degrees, I tested the temps against the grills readings using a calibrated pit probe mounted less than 2 inches from the grills built in control probe. I am attaching the graph from the test session. It ran at 3 different temps, 250, 350, and 450. It shows the data supporting the summary I put above. I'm also attaching pics showing the location of my monitoring probe in relation to the controller probe. I need your assistance in resolving this issue to be able to grill and bake on my new Traeger.