When I put my '70 malibu into drive or reverse (auto transmission) it idles so low that if i don't gas it, it'll shut off. Do I have some sort of problem here?

Could be a few things. Curb idle speed could be too slow . The timing could be off a few degrees. The carb or intake might have a vaccuum leak or car could be flooding. Choke malfunction. These are the most common things to look for.

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Malibu 307 (aka 406 smblk)
69 SS 396(aka 454)
Wolf in sheeps skin

Okay, thanks for the tip, buddy!