My transmission slips?

When you replaced the water pump did you remove the radiator? If so, your transmission could be low on fluid but to be sure check out this instructional guide with the specific instructions below to help you on your car.

https://www.2carpros.com/articles/how-to-check-and-add-transmission-fluid

Check out the diagrams (below). Let us know what happens and please upload pictures or videos of the problem.

10. Fill the transmission to the proper level with DEXRON(R)III transmission fluid.
11. Check the Cold fluid level reading for initial fill only.
12. Inspect the oil pan gasket for leaks.