I have a 2010 F350 gas. Should I be able to use tow haul and 4WD at the same time? If I use 4wd high or low, the tow/haul light goes out. I asked the ford dealer and they were unsure if the two would work together since both function to adjust the transmission. Any thoughts? no codes

 

Since 4WD, on your vehicle, is meant to be used on slippery roads and not recommended on dry roads You probably can use 4WD to park, or tow maybe from a ramp or steep take off spot, but I don't believe it is recommended for regular driving on dry pavement.
Did you check what your owner's manual instructions might say?

 

More info... I had a trailer of hay behind truck ~11,000 lbs. I had to descend a steep grade in hay field to get back to the road. I do not use 4wd while towing on the road.