hydraulic lifter problems

What cam are you running? You didn't say. There are a lot of flat tappet comp cams. Unless it's a really big one that's about all your going to turn with a 360. 6100 RPM is spinning pretty darn good for a 360. Why do you need to rev higher? Are you running forged pistons? It's not a good idea to spin much over 6000 without them.