I would replace the tee's as well. You can by the tee's and the hose end quick couplers all individually without hoses. If never replaced the hoses i would change those too. If buying aftermarket use Gates. DON'T use the Doorman ones. They're junk and don't fit properly. Other than that use the OE ones. I like the idea of the alluminum ones the other members posted up as well.
At first, I was not going to replace the 'T's, since it was such a PIA to remove just the heater hose couplings from the 'T's. But, after many folks here replied, strongly recommending that I replace the 'T's as well, I did go ahead and replace the 'T's with GM parts, and not Dorman parts (again, at the strong recommendation of folks here).
That is what makes this Forum so powerful and helpful. Knowledge is power, and it helps to not have to do the same job twice or more, because it was not done 'completely' the first time.