tow/haul mode on 07 new body style

My 1/2 ton '07 has a tow/haul button but I can't seem to get it to make any noticeable change. when i bought it a couple months ago the salesman said it would only work when it felt a load. in the manual it said something about 75% of the payload or something like that. this should probably be enough confirmation for me, but i guess i wanted someone who knew to tell me it won't do anything unless i'm towing or hauling something really heavy. i was going down the interstate at almost 80 mph, had a couple hundred pounds of stuff in the back and a topper, with a full tank of gas and my wife and two kids in the front (probably close to a thousand pounds total over the empty vehicle weight). i went up a hill with the cruise on, put it in third and pushed the tow/haul button. nothing happened that i could notice, other than shifting to third. i'm guessing this is normal from what i said above, it was just surprising that the truck was so reluctant to go into that mode. my friends '06 will do it whenever he pushes the button.

I have 07 ext cab 2wd 5.3 . I don't know about changing to the tow/haul mode while on the highway at speed, but if I change to it at a stop or very low speed, I can feel big difference in shift and RPM. Chuck

when hauling heavy load like 1000lbs you should keep the speed down to 70mph max.

operating in 3rd gear is good. but at 80mph the rpm is quite high. tow mode will not drop you down to second gear !

when operating at lower off highway speed , tow mode will delay upshifting to lessen transmission damage. operating in 3rd gear keeps the transmission from overheating..

tow mode at below 50mph on steep hills / mountains will also cause the upshifting to be delayed. if this is not working you could have a defect..

ya, i definitely didn't expect it to shift to 2nd at 80 or I wouldn't have done it. i guess i don't understand it that well. i also think i have a very high-geared diff, which i haven't checked yet. it just seems that at highway speeds hills are just too much for it. i'll have to play around with it more. hope there isn't anything wrong. thanks for the responses.