It has just branded around the frequency since it flipped to CHR in the 80s ("97FM" originally and then to "97.5FM" in 1991).Speaking of Waco I always found that IHM 97.5 which is CHR has no monkier besides 97.5 I'm surprised it isn't called 97.5 Kiss FM.
Before it flipped to country WACO-FM, 99.9 was short-lived AC KTKS "Kiss 99," using the KTKS calls previously on 106.1 Dallas during its 1980s "Kiss" days.
As KWTX-FM covers both Waco and the Killeen/Temple markets and Killeen has KSSM 103.1 "Kiss 103.1" since 2000, I suspect that has blunted the desire to brand KWTX-FM as "Kiss FM."