Hi Chris, find out if your mechanic checked the "basic position" of the new lifters. This is required when rockers and lifters are replaced. A special guage is required to measure the height of the ball which the rocker arm fits over. If found to be out of spec, shims are available in various sizes to correct this. The shim is between the valve side of the rocker and the spring retainer. This is standard operating procedure when performing extensive top-end repair. Good luck and let me know how it goes.