First off, from what I read, only the early non-WiFi Traeger controllers seem to have this issue. You don't say what style you have but I will assume it is one of the vertical rectangular non-WiFi enabled controllers. Traeger apparently completely redid their control algorithms for the WiFi unit and got it right the 2nd time.
Unless you have a very special controller, there is a hidden function built in to most controllers called a Pause function. It has 6 settings ranging from P-0 to P-5, with P-0 being short and P-5 being long pauses between pulses of the feeding auger. These only appear to come in to play when the controller is at or above setpoint, meaning trying to hold a constant temp. Traeger controllers come set at P-2. This function exists in most controllers but is hidden and to access the button to change P-settings one has to physically remove the controller by removing the two retaining screws and gently pulling the controller out of the hole. The button is located in the upper right side of the controller. The unit has to be powered up and first press will cause the display to show the current P-setting, further presses advance the P-setting through the range.
Ok, there seem to be massive differences in aftermarket Traeger controllers. My controller died and I purchased an Amazon replacement for about 1/5 the price Traeger wanted for ostensibly the same unit. At a setting of 180 F it would sit there and ramp up to near 300 F. It flat would not hold a temperature setting below about 300, completely unacceptable. I wondered if it was programmed for a much larger unit but on looking realized I have a large unit. I learned about the P-settings by viewing a Youtube video and reading. Google 'Traeger P Settings' to find this data.
I went to Temu or Aliexpress and found a controller that showed an accessible button on the front to change P-settings. This controller out of the box was head and shoulders better than the Amazon unit and once I moved it to a P-5 setting it now seems able to control to temperatures of 225 F reliably. I can't get it to hold 180 F and cold smoking seems to be beyond anything I can get this unit to reliably do. The Smoke setting still seems to ramp up to fairly high temps for no obvious reason.
A WARNING: Traeger does not advise using the P-5 setting as the fire can partially go out allowing a buildup of fuel and then catch leading to a serious runaway or overtemperature situation. I only run mine on P-5 when smoking at low temps where the smoker is monitored and then set it back down to P-2 or P-3 when cooking for long periods. Do be aware of this potential hazard.
Attached are a couple articles I found discussing P-settings.