I see you've thought about this.
I've just seen one too many winters with icy roads and cars being stuck and (temporarily) abandoned making roads between towns unusable for a while.
I imagine that but worse with everyone fleeing the city and getting turned, being unprepared for a journey, running out of gas all over the place - not just cities. Maybe they can go off-road and get around a perpendicularly abandoned vehicle or two but eventually there will be an obstacle no truck can bridge.
So for me, I think two wheels for mobility. But that would also depend on what kind of zombie and what kind of apocalypse. Are they fast or slow; do they hunt by ear, sight, smell; is it almost instantaneous or after a year-long pandemic, do they travel in pack or avoid each other, how do they perish, etc.
Are you sure you're underperforming, or is that just an idea you came up with yourself? Have you talked to a boss or manager about their expectations for your role and if you are meeting those expectations?
It may just be a self-sabotaging thought, and getting confirmation that you are meeting expectations could let you relax and work at a preferred or natural pace without stressing about your performance.