losing fuel pressure
 

My '98 Shabah with 7.4 Bravo 3 won't run over 2000 rpm under load. Put fuel gauge on her and shows a steady 38 psi with key on and at idle. Motor will rev to high rpm by itself, but fuel pressure guage will gyrate quite a bit. But when I take it out on water and under load it holds fuel pressure, until I reach 2000 rpm where the fuel pressure goes to almost 0. Throttle back and pressure returns and will idle perfect.

I replaced fuel filter/water seperator, distributor cap and rotor, and put the appropriate amount of sea foam in fuel. I did read on web blogs about similar problems and a filter screen at the fuel regulator getting clogged. My fuel pump and regulator are located in a small plastic box on the lower side of the block. Can't get the cover off this box as its up against the fiberglass hull where mtr mnts are fastened. Does anyone know how or if this cover can be removed??? Thanks for any help.