Car Revs in neutral but sputters at 3500 RPM

[D-rock]

I did a search couldn't find anything.

Car was working fine on the highway then started sputtering at 3500-4k rpm

I can drive as fast as I want just have to change gears before 3k, if not car will bog but pick right back up in the next gear until 3k again.

Also car will fully rev in Neutral and ideals perfectly


New fuel filter and fuel pump works fine. M50 engine

Any advice would be appreciated

Thanks!

-Derek