I wouldn't think there would be any difference between a 5spd or 6spd, but none of this weight rating stuff makes sense to me anyhow. On my 99 5spd, the sticker said GCWR was 16000lbs. Didn't believe that so looked in my owners manual. You're right, manual doesn't provide anything for my transmission/rear end configuration. After much TDR discussion, I finally called DC, gave them my VIN#. They told me my GCWR was 20,000lbs. Said they would send me something, but never did. Too late, my GCVW is right at about 19600. I have absolutely no problems pulling or stopping!