Convert 2008 Base 2X4 Highlander to Limited Slip Diff.

[Iluy]

I have a 2008 Highlander, V6 with a Toyota factory tow hitch, which I had them add to the vehicle before I took delivery. I tow a 22' Center Console fishing boat. The vehicle has more then enough power to tow just about any where.
I live in Florida and I have many boat ramps to choose from when I go out to fish. Now, I've noticed on occasion that when loading the boat and I start to pull it out of the water that I get the rear wheel to loose traction and spin, especially on some of the more steep ramps. Not always but I have to basically let the vehicle start to move forward with very little acceleration, if I give it a little to much, it slips.
I'm thinking I can add some heavy load shocks in the back to help, but I really think I need to change the open rear differential to a limited slip differential.
So, has anyone done this on thier vehicle and if so where should I go to get it done (off road shop, transmition shop, race shop or just order parts and have a shop do it)?
Thanks in advance.

[jimmied]

i think you need to reword your post. I am confused as to why a rear wheel would spin on a 2wd vehicle.