Hi!
No, your TV is actually 720p.
http://reviews.cnet.com/projection-tvs/samsung-hl-r4266w/4507-6484_7-31335747.html
I confirmed this at Amazon as well.
I don't think the problem is with your TV. The HDMI input should automatically reset themselves based on the supported signal coming into the port. That's the beauty of HDMI. It sounds like the problem is that when you selected 1080p on the DVR, it stuck and now since you don't have display on your screen, you can't put it back. My experience with this unit (and I've had it for 5 years) has been when you unplug it, it goes back to transmitting ALL resolutions and if that doesn't work, call tech support at the cable company and have them reset the DVR remotely. This should get you back to normal (I'm really surprised that they didn't suggest this).
That is assuming that yours uses Passport Echo interface. Most providers who use the SA 8300 have switched over to the Passport Echo interface but if yours hasn't (which would be odd considering that their boxes are now handling 1080p). If you don't have the new interface, you're going to have to have you provider walk you through the steps to manually reset your DVR back to the default settings. It can be done with a combination of buttons on the front of the DVR, i jsut don't know how to.
I'm very curious as to who you cable provider is because the fact is that there are no channels, major network or cable, that transmit their programming in anything above 720p/1080i due to the incredibly high bandwidth that a 1080p signal uses. Cable companies lack the infrastructure to handle that amount information. If your DVR's software has been upgraded to support 1080p resolution, it must be up-converting the 720p/1080i signal.