This truck has a 355CI blueprint engine. The customer complained of a misfire and a slight ticking sound. Upon inspection we found two cylinders misfiring. We performed a compression test and it seemed high. We removed the valve covers and placed pistons at TDC ( Top Dead Center) found rocker arms were too loose on intake side of #1 and #5 cylinders. We removed the rocker arms and push rods and looked into the cavity where the valve lifter is and attempted to remove the two affected lifters, they would not come out. We removed the intake manifold and found the Camshaft had worn down the intake lobes on the affected cylinders and the lifters had mushroomed. This is usually caused by lack of lubrication or lack of proper break in. We tested oil pressure and volume and found no issue. Customer opted to replace the camshaft and the lifters, flush the block of any metal residue and put break in oil in the vehicle. We found that the oil used previously had not contained Zinc and may have been part of the original issue. We suggested the customer use an engine oil containing Zinc or an additive every oil change. The engine now runs smooth and without any problems. 1,000 miles later and still no issue.