About 10-years ago I transited the Tenn-Tom, mast up, from it's head at the AL/MS/TN line, all the way to Mobile AL. Mast head was 32.5 ft., plus another 3' for VHF antenna. (Actually I did the entire run from Channohan IL (Joliet) mast up. That includes the Illinois, Upper Mississippi, Ohio, Cumberland, and Tennessee Rivers.)
For all the reasons cited by others, don't even think about cruising on the lower Mississippi (that is, from Cario IL south).