Re freq, as Rainman says, the receivers are all a bit different, and also your LNBF will drift a little bit.
But since your freqs are showing 11715 and not 10715, then my guess was wrong, so it must be like Rainman said, that you just don't have enough signal strength, although it is very strange that you can get 99% quality on Tips, and not have enough signal for
PBS. I don't get that good a signal on the two channels you're getting, yet I have no problems at all on PBS.
Only other thing I can think of is signal loss in the coax, as this often tends to affect the higher freqs. How long is your coax, (although length is seldom a problem unless it's over 200'), and what kind of coax is it? If you have reasonable quality RG6, this shouldn't be a problem either, unless you got water in the coax or something, however if by chance you're using cheaper cable, like RG59, and have a long length, then I could see you losing the higher freqs.
One other thing, that I've seen on the Ultra, is that if you did the Power Scan using the "Symbol Range"="FULL", then sometimes it will miss transponders.... at least mine does. I usually do a scan with the high setting, and then again with the low setting, and it usually finds things.
The other thing you should do, is go into the TP scan (transponder scan). Check to see if the PBS transponders are already in memory, if not, back out, and go to edit TP/SAT , and edit the transponders by selecting NEW, then enter the data for the PBS transponders. After you've done that, go back to TP scan, or if the transponders were already there, then select one of those transponders in TP scan, and see if you get signal and quality. If you get quality, then hit OK, and it should scan in. If you don't get quality, then you still have problems, either with coax or alignment or something.