Nu Relic power window issue

[colorado80439]

So I've installed a complete set of Nu Relics power windows in a 69 Camaro coupe and I have to say I'm pretty impressed. There is one issue I've been trying to solve. The door windows power/roll down too fast for my liking. Up speed is fine and quarter windows are awesome. I've spoke with the folks at Nu Relics, they are helpful but do not have an answer. I installed a 10K potentiometer rated for DC, which slowed the window speed but burned up in the process. I think I'm on the right track with a variable resister to control the down speed, just not having much luck finding the correct product.
I'm thankful for all the help I've received from everyone on this site.
Thanks again