First of all, your Ironwood was set to 165F, but do you have any idea what the actual cook temperature might have been? The RTD thermocouples are notoriously inaccurate. You might have been trying to cook at 145F. Get a 3rd party thermometer to check the actual cook temperature a couple of inches away from the cook. I drilled a hole in the lid of my Ironwood and installed an analog thermometer like those found on gas grills and offset smokers. I set the controller as needed to give me the temperature I desire in the cook chamber.
Second, NEVER cook based on time and temperature. It rarely works out. The recipe time and temperature is for planning purposes only. When cooking beef, a 5 degree difference in final temperature can make a big difference in the outcome of the cook. Thus, get yourself a decent instant read meat thermometer. With something like a Tri-tip, you will want to check the temperature in several spots, so make sure you get one with +/- 1 degree accuracy and a read time less than 3 seconds. You do not have to spend a lot of money on one, but don't get the cheapest one on Amazon. .
I would suggest setting your controller to provide a cook temperature of 225F as measured independently. Cook the Tri-tip until the instant read thermometer reads 125F in several places close to the center of the roast. Then finish off to final temperature by searing until the desired internal temperature is reached for your preferred doneness.
The Traeger does not really get hot enough to sear beef, especially if the actual temperature is below the controller setpoint. I have to set my Ironwood at 460F to reach a cook temp of 400F and that is not really hot enough. Some people purchase GrillGrates to help with the searing process. I got a set for my Ironwood:
However, I was still not satisfied with the results, so I purchased a gas griddle to do the job properly. You can also do the searing in a skillet on your kitchen stove.
I recently posted the results of cooking some thick steaks on my Traeger and finishing on the griddle. Perhaps you will find that helpful. The process is the same for steaks as well as roasts, but the cook times might differ.
I’ve never even heard of an onion bomb
www.traegerforum.com