Why at Low accelling runs fine, high accelling runs rough, no power?

What is your question?

My 2003 pontiac bonneville se has very little power at high accellerating and acts like it wants to die. At low accelleration it runs fine. Why is this and why does the car seem to get louder? Car acts this way when driving, and seems like the exhaust gets louder and pipes and muffler and cat.converter is fine.

What makes this problem better or worse?

Is worse when engine is cold, when warm no high accelle

How long has your 2003 Pontiac Bonneville had this problem?

3 weeks