2013 Silverado 5.3 Stuck Lifter

What are your thoughts on running the truck in M5 gear as a way to prevent the AFM system from engaging? I currently have a collapsed lifter on #1. Not sure if it's the intake or exhaust as I have not yet pulled the valve cover. Dealership and other mechanics are recommending a complete valve replacement ($3000) or motor replacement ($6000). I feel that if I can get the lifter freed, I can run the truck in M5 gear since I do 99% of my driving locally. If I do the VLOM mod and sleeve the oil pressure tube, would that allow me to drive normally ( in D ) without additional modifications? Thanks!