Is 3" exhaust to much for a 318??

I have headman headers with a 3" collector, 3" "H" piping into 3" flowies dumped right before the diff...

I bought the car this way, it sounds fine at a higher RPM or right when i come off from idle (nice, strong and pronounced), but inbetween the two it's kinda choppy and loses almost all it's tone......

I was wondering if maybe my exhaust is to big for my motor (318LA). The only mod i have besides the exhaust is a mild cam.....

Thanks!