I suggest a better antenna and preamp , Winegard HD7082P antenna , Winegard AP8275 preamp on the 40 foot tower. If this does not do it then you will need to get the antenna to 65 feet. The preamp needs to be mounted just below the antenna. I went to the >Start MAPS< part of tvfool and put in different antenna heights , 65 to 75 feet are heights that the NM(dB) noise margins improve a little and the ground reflections are less. At distances of 70 + miles heat in the air blocks Tv signals and the out right strength of the sun just blasts away at the weak Tv signals. . And also the 1 and 2 edge land path obstructions do not help any.
http://www.solidsignal.com .
http://www.starkelectronic.com