Agree with Jerry, I would absolutely make sure your fluid level is good, and drop the pan to inspect before I undertook the job. When you say "slipping" do you really mean slow to engage? Or legit slipping, input RPMs don't match the output speed?
The good news is that a rebuild is absolutely a job you can do in your garage if you have a decent attention to detail. I had never opened up a transmission before but successfully rebuilt mine last summer. The FSM & the ATSG are pretty much invaluable resources. There's a long thread here detailing my misadventures during that process. I also video'd a lot (but not all) of it. I too wanted to add this to my list of things that aren't a big deal, mission accomplished.