1970 Mercury 500 running rough

[1958scottguy]

I have a 1970 Mercury 500 which seems to run very rough at high rpms. It will only get going about 5-10 mph and while doing so the engine shakes like crazy. So far I've cleaned the carbs, put new carb kits in new fuel lines and new fuel pump kit. After doing that it still ran rough and only went 5-10 mph. So I checked the the timing with a timing light and it is running at full throttle around 45 degrees even with the spark advance screw retarded all the way. It should be at 35 degrees. Also at idle it was running at 15 degrees. Yet it runs perfect at idle. Any ideas? Thanks.