rustorbust

I cant figure out what is up with the motor. I have a 1976 280z that has an original l28 engine. It has the original fuel injection. When i have the throttle wide open it looses power after about 3700 RPM's, it doesnt loose all power but there is a very noticable amount. It hasnt done this forever but hase been getting worse recently. I have the timing set right so i don think that is the problem. I was wondering if maybe it could be the fuel pressure. Has anyone had problems similar to this. Little help please. James B.