Different idle speed for D and R?

Chev Impala 2001, 3.4 I just bought a few months ago.
When changing gear from P to Drive, the car can hardly move, or move very slow. I have to press gas pedal to get the car move forward. It's not like
any car I ever used. However, if switching from P to Reverse, the car backs up pretty fast (or say, normal). Is it a problem? or a kind of factory setting? Is it related to idle speed?
Thanks for any advice.
Simon
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very
like
backs
Nothing wrong. Just a different gear ratio for reverse versus drive. Engine can move the car easier in reverse.
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