Need help troubleshooting idle issues and stalling [2001 Chevy Blazer LT 4WD Automatic]

Hi all,

I started my car when going home, and before driving, I turned the A/C on, however this made the RPM drop by a almost 300RPM. It would bob back up to about 600, then drop again.

When I started driving, whenever I would slow down, the RPM would drop significantly and eventually the engine stalled out. I turned off the A/C and drove the whole way home while manually staying in 1st and second gear to keep RPM high, and when I stopped, I shifted to neutral keep the engine running, though I don't know if that kept it running or if turning off the A/C was enough.

Can someone point me in the right direction so I can start troubleshooting?