I personally haven't had any issues with the TC4 or TC5 shocks. I guess I was lucky with my TC4 shocks when I used them.
Anyway, if you do upgrade your existing shocks there are two ways to do it. You can get the upgrade kit or you can purchase the entire thing.
There are people who absolutely love the Tamiya, Xray and Losi's new 10mm shocks. I have only used the Losi's and I thought they were an improvement over their previous shocks.
I never liked the green slime, I just used a lot of shock oil when putting them together.
Nonetheless, the choice is up to you.