2005 Dodge Magnum Poor Performance

I have had my Magnum into three dealers now and they say nothing is wrong. Under factory and extended warranty. When I am going up slight hills/inclines, or even on flat surfaces, the engine will rev, RPM's increase almost to red line, but the car hardly moves and when it does, it's very slow.

I have been told the Transmission is fine, no trouble codes, EGR has already been replaced. What could this be? It gets alot worse when the AC is on, almost unbearable fo rgetting on the interstate because acceleration is lagging.

Also the shifting is rough, clunks and jerks.

When this happens, the engine will make a different sound. Kind of like a deep V8 growl, much different then when it's moving normally.

Any help is most appreciated!

Thanks!