My setup is uses a DCT Multimedia drop amp (indoor use only) with freq. bandwidth of 54 to 1004 Mhz. mounted indoors 30 feet away from TV and 50 feet away from attic mounted yagi antenna.

The CM 7778 has some what lower gain and two inputs, one for VHF and one for UHF antenna OR combined for one input only. Lots of options and based on your antenna setup. This one will less likely overload on any strongers signals.

Before going on the roof, you could always try the pre-amp indoors and see if it helps first.

Your 18.1 channel @55 reading sounds like a multi-path or reflection is interfering, rotor could clear that up. A tv ATSC tuner should still work at signal level of >30 if noise is low and no interference.

My thoughts.