First, how are you measuring the temperature?
The RTD thermocouples that provide temperature feedback to the controller are notoriously inaccurate. I drilled a hole in the lid of my Ironwood and installed an analog thermometer such as found in gas grills and offset cookers. I also have a digital probe that I can locate near the cook, but not touching either the meat or the metal grate as that will cause false readings. That will give you a much better idea of your actual cook temperature. The device you use does not necessarily need to be expensive, but it does need to be reasonably accurate.
If you were to place a thermometer inside your kitchen oven, you will find that the temperature does not remain at the setpoint. It will drop below the setpoint before the oven will turn on. Then the temperature will climb above the setpoint before the oven will turn off. In an offset smoker, when wood is added to the fire, the temperature will increase, only to fall again as the wood is consumed.
Traeger indicates that variations in the temperature around the setpoint are normal as they are trying to simulate the operation of an offset smoker. That variation causes changes in combustion of the wood pellets that creates differences in the smoke and contributes to the flavor of the cook. Do not be concerned with a +/- 15 or 20 degree F swing in temperature. If you see a difference of +/- 50 degrees F, then something is wrong.
