2001 silverado 4.8 po121 after cam install...shifts funny HELP!!
my son has a 2001 Silverado 4.8 we installed a tr 224 cam and a set of 243 heads,3600 fti converter headers etc etc...having a problem with a code po121 and the transmission shifts funny...I know on hpt u can disable the code but how do you correct it so the transmission will shift back to normal...thx