Channels 2 thru 99 generally don't use the cable box so they can change quicker and without problems. Above 99 need to change the channel on the cable box so they will be slower. There is also a chance for missed channel changes due to IR issues. Do some tests by manually chaning to higher number channels, watching the channel changing on the cable box, and see what happens. If it misses changes sometimes you may need to change the IR setting to do slower channel changes. You do that somewhere in the Setup menu, but I am at work and can not look up exactly how to get to it.
For of all sad words of tongue or pen, The saddest are these: "It might have been!"