2001 Chevy Impala clunks upon accelerating from stand-still

Does it feel like the transmission is slipping? Can you give me somemore information.

The transmission fluid may be low. Unfortunately this is not an easy thing to check on these.

If you can get a scanner to read codes, there may be a transmission one related. Hard to say. Should get the level checked first and look for possible leaks. I can go through the procedure, but you really need a lift to do it.

I got your PM. IF you are sure this isn't a transmission issue than there is somthing physically holding the car back.

When this happens, does the engine idle raise like it should? Or is it non responsive to the idle as well?

Are the rear brakes drum brakes? Have there been any abnormal braking qualities such as a lock up or longer than normal stopping distances or a harder pedal?