The beauty of buying from Costco is the liberal return policy, that said what issues are you having? Most of the major issues being discussed are with the new D2 Wifi controller. I've heard nothing but good reviews about your unit.
So far as the probes are concerned, the Traegers and most of the competition are type K thermocouples in a steel 90 degree capsule. The Traeger probes are no better or worse than others (type K) My Weber bluetooth probe set is the same type K with a slightly larger jack. My Omega HH-22 is a 2 channel type j or K thermocouple with a few test features it can read pretty much any type j or k thermocouple. l used to make up my own probes with type K wire and before I started a test (I was a troubleshooter for large refrigeration systems manufacturer I'd always check accuracy using ice bath or boiling water).
What we're doing with smokers and pellet grills requires more monitoring than a home kitchen oven. With the cost of product and time spent it's always a good idea to be able to count on your tools. Thermocouples and other probe technologies are head and shoulders above cheap bimetal oven thermometers. Do what I do, I wipe the probe and wire. Coil; them and put em in a zip lock with a cup of uncooked white rice. It dries up any water in the capsule. Consider that the probe tip is in the meat at a temp considerable lower than the grill inside cooking temp (steak 37-150 degF, grill temp 225-450 deg). Migration happens, vapour from the hot end of the capsule will condense in the cooler part of the capsule in the meat.
What is wrong with your display? If it isn't right order a new one, you have 3 years of liberal parts replacement. The RTD's on those models is very accurate.
You mention pellet feed, what are your issues. There are enough people here that live and breath BBQ, someone will have an answer
So far as a P setting, that's very over rated. I live in Canada and it was a help in the fall and winter but in South Carolina it shouldn't be necessary. I had it and I played with it. It's the nature of the beast, I'm a nerd (techie)
I apologise for being so anal about probe accuracy. In my job as a Refrigeration Manufacturers Field Rep I had to go nose to nose with a few health departments about product and supply air temps. It usually wound up that I'd prove their equipment was inaccurate. I also felt it was my job to help the customer and their contractors get the most out of their equipment. That's why I have such disdain for $3.99 bimetal thermometers.