Hmm, I use the New-Relics power windows in my car and they only draw around 2A when moving up or down. When the window hits one of the stops the current will shoot up. I have my over-current limit (stall) set to around 3A on my automatic up/down circuit.
I don't recall that they gave the current limit specs when I purchased my motors, I wonder if they did change to a different motor.
I think you are right that the low load is window going down, high load is going up and stall is when the window reaches one of the stops.
You probably should design around the 5A low load spec when choosing the resistor, but know that current can get as high as 20A if you leave your finger on the switch too long after the window hits the stop.
I would shoot for a variable resistor under 10 ohms rated for 300W or more. Like the
AVE030020E8R00KE. Try it without the diode first you might get lucky.