1990 Mercury XR4 150hp. I replaced upper housing assy., t-stats, poppet assy., and I still have 28-30psi at 5000-5500rpm's. What else could cause this? Before the changes, I was at about 25psi wot, now I'm almost pegging the gauge. Please help me if this is even a problem, I've never seen pressure this high on any Mercury I've owned or worked on. There's no overheating, but I'm scared I'm running too cold unless I idle. Thanks.