automatic 94 Jimmy shifting problem?

I am brand new to driving, and have just turned 17, I recently purchased a used 94 jimmy. I don't know much about cars so don't be annoyed by my most likely dumb question.

I had the gas tank, and the sending unit on the fuel pump replaced a week ago.

I started my car today and there was a problem, the car wouldn't shift into gear. It would start at the first gear and would not reach second until about 20 seconds of struggle. shifting from 2-3 there was the same problem, and so on.

I was able to make it back from school ok. but then when i tried to start the car again it would just stall after 10-20 meters.

any suggestions would be appreciated.

Any SES codes? Make sure your TPS is plugged in and operating properly.