I have a '96 Merc 350 4 bbl. Last season I had a problem when I ran WOT (4600) for extended peoriods. The engine would slow after about a minute and then it sounded different, more hollow and louder. After shutting off for a minute, it would be okay until WOT. So I just refrained from running WOT towards the end of last season. I would like to fix this spring. I have checked oil level, changed oil weights, tried SEAFOAM, all with no success. My thought now is it may have been a hydraulic lifter pumping-up and holding the valves on one or more cylinders open. I was going to replace them this spring. I was planning on using CRANE "Anti-pump up" lifters. I think $100 a set. Will these work and how easy are they to change? Let me know your thoughts and experiences.<br /><br />Thanks<br />CP