The DB-8 and CM4228 are not so different that I would expect any improvement.
If you can't mount any higher and you've gone through all the iterations of aim adjustment (including changes in elevation and location), then two antennas to consider are the Antennas Direct 91XG and Winegard HD9095P. The two products compete for 'highest gain' in the consumer grade UHF antenna market.
Your other options include: consider a tower, commercial grade antennas or custom built.
Looking at the path profile of CBLT-DT, it looks as if a little more height may pay big dividends.
http://www.tvfool.com/?option=com_wr...LLTV2%26n%3d16