2001 GC problem, total novice, please help

Ok, just looked it's a 4.0L, I6 engine. When I use the brakes this occurs. It's like when I press or release the brakes, it kind of lurches forward and feels like something is sliding forward from the back. I'm sorry, not car savy, & hard for me to explain. At first I actually thought the spare tire was loose or something but it's not. It doesn't do it everytime I use the brakes but quite a bit of the time.

Also, I think the transmission is slipping a bit here & there. I guess I'll have the fluid changed, but anything else I can have done or do to stop any major problems?

Any help would be IMMENSELY appreciated.

Natalie

Anyone?