It idles fine, comes right up on plane but about 3200 rpm it just dies. pull the throttle back and it runs fine. Cuts out if you run the rpms up in neutral or under load. What to check??????

First I'd check fuel pressure then cap and button just for simple things first off

Do you have the fuel pump thats mounted to the impeller? If so take apart & check the cam & the arm on the pump.

Seems a bit like power reduction mode (that'll let you go to 2800rpm then will drop 4cyls until it's below 1200 rpm--or something like that). I'd also suggest checking timing and condition of cap/rotor.

Today I replaced the cap, rotor, water sep/fuel filter, checked all the grounds and clipped the tach lead. if anything it now seems to be worse.

Check your Vapor Separator tank, there is a fine micron screen in it that gets clogged the more you apply throttle. Clean the screen and tank. Had this happen on my boat.

on my eng theres a brass check valve by the fuel filter it was cloged with fuzzy stuff thats in the tank ,my engs would pulsate starving for fuel at 3000 rpm and above under load- its fine now but is checked on a mounthly basis