Engine sputtering when transmission is shifted into gear

We need to check a couple things to see if we can get more info on this and which direction to go.

Let's start with checking the fuel pressure when this is in park and then in gear.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Basically, it should stay steady but may bounce a little bit. However, if it drops then this could be the issue.

Next is to check for a vacuum leak.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

If all this checks out, then we could have a motor mount issue or even a converter issue.

However, let's get to that when we check these items out first.

As for the mount, the engine should not move much when putting it in gear but if it is rocking then the mounts are shot.

https://www.2carpros.com/articles/replace-motor-mounts

This would not cause the engine to run poorly, just vibrate so if it is actually running poorly then we have a different issue.

Let us know what you find with this info, and we can go from there. Thanks