So two times ago when I went out my Tow/Haul button was working intermittently, last week when I went out it didnt work at all. A quick google search and I found out many folks have an issue were the wire just gets worn and breaks apart from the daily stress of moving around. I pulled my column apart tonight and sure enough it was broken. I spliced and soldered the wires back together -- they are darn small - like 20g. Not sure how long it will last, but we will see. Next time it goes out my guess is I will need a new shift lever assembly - it runs about $75.
Here is what it looks like -- there is a little orange wire coming out of the shift lever that runs down the column and plugs in to a socket under the dash.