That happened in late 1997. I remember this because the station was still WTDR in Summer of 97 when they carried the audio for the free Garth Brooks concert in Central Park. It was later that year that they changed their name. Tom Jeffries was the first new jock I heard on the air with the new format.
The last jingle package they used with the WTDR calls was Jam's "Hot Kiis" package. When they changed to Kat Kountry, the new jingles were slower and kinda sounded like a black church choir. Seemed odd to me, but apparently it worked.