Yes, one of the first thoughts that comes to mind is, there are differences between tuners. Some can tolerate low signal quality better than others.
Then, the CS4 is a great UHF antenna. However, it is not intended to serve well as a VHF antenna. I'm quite curious to know which signal(s) are giving you trouble. If they are real channels such as 8 or 10, you'll need to consider the use of a High-VHF antenna. This could be your source of quality trouble. I'd suggest the Antennacraft Y5713 + a UHF/VHF signal combiner. Also, Antennas Direct offers a dipole option,
http://www.antennasdirect.com/store/...-Assembly.html
http://www.antennasdirect.com/store/...Combiners.html
To answer your question re. amplification as a fix... You have plenty of signal power in the air. An amplifier could overload, leaving you with less reliable reception.
http://forum.tvfool.com/showthread.php?t=13646