2000 Oldsmobile Silhouette - Shuts off

my tranny turns off the engine when I put the shifter in drive or reverse.

With your foot firmly on the brake pedal, slightly step on the gas pedal to bring the RPM’s up just slightly and then shift into gear.

If the engine doesn’t stall, there’s a problem with the IAC valve.

https://www.rockauto.com/en/catalog/oldsmobile,2000,silhouette,3.4l+v6,1359266,fuel+&+air,idle+air+control+(iac)+valve,6072

Tester