P1870 xmission code

Hi There GMC gurus...i have a 1999 GMV Jimmy and the "check engine" light came on. it was diagnosed with a xmission problem, code: P1870. I was told i needed a xmission rebuild. i was told the gears were slipping. true? car runs fine. i'm taking a long trip this weekend, can anyone advice of possible problems. anyone had this code before?


Thanks!