chrichri

I am building a 1978 nova with a factory 305 with 75000 original miles. It came with a 2bbl setup stock. I started having a fluttering issue with it so I went through the whole fuel system(fuel pump, filter, carb, then a new 4bbl carb, then a new 4bbl intake) A few other performance parts(ignition, radiator, dress up stuff) then I checked my valve springs. Everything I have done has helped but nothing has fixed it. It continues to stutter at 90ish I was not going to worry about it because I was building a new motor but now that has gotten slowed down and I am finishing the body work first so I want to fix this problem. Is it the camshaft getting rounded or the valves are sticking or what? Please help