Hitting a wall at 4K

I'm had an issue crop up on my 70. Whenever I hit 4K rpms (any gear) it stumbles pretty hard like its got a rev limiter on it. I initially thought it was an ignition problem until I pulled the plugs and saw that they were kinda white. I am running one of those clear parts store universal filters and I noticed a little bit of rusty looking junk in it. When I pulled it out and cut it open there really wasn't anything to speak of in it. I put a new filter on it and it didn't help. Still has the factory tank and lines in it, is it possible that the little filter assembly in the tank has collapsed on me?

Thanks