I picked up a new 2023 UForce 1000, I was working on installing a turn signal kit (aftermarket XTC), and I am realizing that I have no tail lights. Brake lights work, but tail lights never illuminate. Switch between running, DRL, headlight, low, high etc, never any running lights.

I am hoping its just a plug somewhere not seated perhaps? I tried the main harness under the bed. Unplugged and replugged. All fuses are good.

Any ideas? I don't have a trailer for it at the moment, so going back to the dealer is difficult.

After I bought the aftermarket stuff, I see there wiring appears to be all in place from the factory. I was going to try to make as many connections at the factory molex under the front cover as possible. I see conflicting info on if the tail and head lights would need to be changed if I just got the factory flasher module, switch etc. Any ideas there also?

Not sure if this is the case, but some manufacturers are now using the brake lights as tail lights by reducing the voltage to get a dimmer illumination when the tail lights are active.  My 2023 Chevy Spark does this sending 9v for tail lights and 12v for brake lights/turn signals.  But this requires a module in the circuit to adjust the voltage.  Since the turn signals require a flasher module that circuit might be in there, and if read your post right you haven't installed a flasher module yet.  A typical flasher module only needs 3 wires, but the flasher module on my 2023 Zforce 800 has 5 or 6 which may be the case on the Uforce 100, so that may be where your "missing tail lights are hiding".