Replace HVAC resistor?

Your truck doesn't have a blower resistor, it uses a blower control module which os the black box attached to the blower motor in your picture. In the attached you will find the wiring diagram. Unplug the harness with the white plug, it should have a Black w violet, Yellow w Green and a white w violet in it. With the key on and blower speed on there should be battery voltage if you connect a test light or meter between the Black and Yellow wires. If you have that then the next test needs a scope but if you have a meter you can connect it between the White w violet and battery, Now adjust the blower speed and see if the meter changes, then try with the meter on the White violet and the Black. Same thing. The White w violet is a PWM signal and usually one connection or the other will show a voltage change, on a scope you could watch it but some meters can pick it up.
If you have the powers and control signal then you replace the complete blower motor assembly as the front control unit isn't sold as a replacement part. The rear one is but it's a different unit.
Now it's possible that there is no signal to the blower module, in that case you replace the dash control unit. That is probably why the price is so high, the list on the control head is $1159.00

So there is no more blower motor resistor in this vehicle, there is a solid state speed control module that is replaced with the blower motor, (all in one) So, I would check the fuse #20 - 40 amp in the fuse panel under the hood first. This video will help

https://www.youtube.com/watch?v=G-xNK79Wa-w

Next, there is a blower motor control relay in the same fuse panel under the hood on the right side. Here is the blower motor wiring diagram so you can see for yourself how the system works. If this is okay I would check the blower motor ground which this guide can help with

https://www.2carpros.com/articles/how-to-test-an-automotive-hvac-system-blower-fan-motor-a-detailed/

Next, the dealer is talking about the FCIM (front controls interface module) which is expensive so I would do these other checks first. Also, there is an outside chance you got a defective blower motor, can I ask what brand it is? Check out the images (below). Please upload an image or a short video in your response, so I can see what's going on. Thanks for the first image.