I had noticed that when I use the auto detect mode it reverts to 720P. The reciever is HDMI 1.4 spec which is strange. So it looks like I'm stuck with this and should report it to VM as an override would be better which saves preferred setting. Another odd thing is that I also own a PS3 which auto detects via HDMI and detects 1080P. I guess my HDTV re-scaled the picture.
So it seems to be a problem I've now inherited after using an AV receiver and a TiVo as the following link suggests after googling......
http://forums.tivo.com/pe/action/for...ostID=10440516
But there is a work around. To hook the TiVo directly to the HDTV and use an optical connection from the TiVo to the AV receiver.