I have an RCA F31672ET and it works perfectly on channels 51 to 98 but will not recognize the rest of the spectrum. I am on cable. Thanks.

Depends on how your cable provider is distributing the TV channels.
Channel 100 is the line into the Jumboband, and most providers don't distribute analog cable beyond channel 99 since it requires a different type of amplifier. They will generally use Digital Cable for higher number channels, which would require a converter box.
http://en.wikipedia.org/wiki/North_American_cable_television_frequencies
Who is your cable provider?