Your cable company wants you to rent one of their boxes so they place many channels on higher ("virtual") numbers, above the 1-125 analog and 1-135 digital channels in your HDTV's or this DVDR's tuner. However, this DVDR will tune those channels, if they're not scrambled, by remapping the virtual channels to "physical" numbers within the tuner's 125/135 range.
This Silicon Dust website might help find your channel relationships. Enter zip code, then select the source (cableco) above the list to see their "virtual" channel numbers and the physical locations on a HDTV's or DVDR's 125/135 channel range. Tune to the physical channel numbers and check STATION AND CONTENT to make sure each physical channel is what you expect.
Of course, your 3575 will only be able to tune channels the cableco doesn't scramble, called the "clear-QAM" channels.
I assume you've done an Auto Channel Preset > Cable (Analog/Digital) as described here?
Here's a help file with more detail.
Edited by wajo - 7/24/12 at 7:35am