About my KT88 Tubes

I am fairly new to analog,tube audio equipment so I thought I'd use this thread to gain some insight on a tube situation that I am experiencing.
My Cary 120S amp uses 8, KT88 power tubes and came with 8 matched Electro Harmonix tubes. Recently, I started loosing tubes from both sides. I would replace them and rebias everything and everything sounded good. I started thinking probably these tubes were getting near the end of there useful life so I chose to replace them all with 2 matched quads of "Gold Lions" which I have heard, were superior. Upon installing them, I am noticing that my top end is very shrill almost to a tinny sound. Do these tubes have a break in period? Does anyone else have experience with these tubes?