I found this out by accident, guess I should have read the manual on my truck, and for those of you that already know about this sorry. I got in my truck and accidently held the tow/haul button with my thumb when I was trying to start my truck and this D with a line thru it came on the cluster, freaked me out. But I learned that it is just the overdrive cancel, so that the truck will not shift into 5th gear. Interesting to me and I did not know, guess you learn something new everyday.

I was trying to put my truck into tow haul right after I bought it. The little light came on and my rpms shot through the roof. I was driving down the highway. I didn't know how to shut it off so I pulled over and turned my truck off. I drove away still not knowing what I had just done. I later read the manual and realized the 03 had this feature. I had only been exposed to 02 and earlyer. The OD lockout works real good coming down steep highways.