tivo s3 hd

I was reading post about hd channels pixelation and freezing, so i turned mine to hd channels and same thing happened to me. Slow load time for guide and channel changing, probably would have rebooted after a few minutes. Non hd channels ok no problems, i have software ver. 8.3. Some people think its a software problems but i think its a cable or hardware problem. Has anybody have a fix for it or should i call the cable or tivo compaines for fix. Any help thanks