Hello, I have a 2001 GMC Sierra 2500HD 8.1L Automatic Allison and I am having a problem when I try to shift into drive, the transmission gear and dash indicator reads as Neutral while sitting in the Drive slot on the shifter column. If I gently giggle the shifter up and down it will then shift to Drive while remaining in the original slot (drive) on the shifter column. Sometimes I have to go to the 3rd gear slot and back up to drive to get it to shift and read as (drive). I can hear the transmission shifting fine when the indicator reads as Reverse, Neutral, Drive, and so on. Yet, it sometimes thinks it is in Neutral when it is in the Drive slot on the shifter column. Do I have to replace the whole shifter column unit attached to the steering wheel because it is sloppy, is it shifter cable that needs to be replaced because it is going back, is it both, or something else?