My mom's 97 C1500 w/4L60E was throwing the dreaded P1870 code, and at the time I didn't have the money for a rebuild. So I changed the fluid and filter and put in a bottle of Lucas Transmission Additive and cleared the code. It worked great! Its been 30k since and no more hard 1-2 shift or P1870 code. I was so satisfied in fact, when I changed my trans filter on my 97 K1500 w/4L60E I added a bottle of Lucas. I've always had good luck with Lucas products.