Taking some inspiration from the GMC car is an interesting starting point, I'm not sure if the grille inspiration is translating though. What is it about the form that you find interesting? Is it the material use, the form, what it symbolizes, etc? Rather than doing a literal translation of the grille onto the shoe can you distill down the essence and rework it to a form that makes sense for a shoe?
Keep sketching, I think it's a good place to start but definitely keep exploring, see if you can do 10 different versions inspired by the GMC car, or maybe new inspirations. Good luck.