the setup I just described above would be very handy in a case like yours,
Because the program actually does an RF sweep of the entire IF spectrum, you'll get a visual indication of the RF Signal strength across the band.
You could compare a sweep as is down the entire length of your feedline,
then sweep again with the tuner closer to the antenna, and compare the overall levels, and ability to lock known transponders.
After a while you get a feel for what it takes, SNR wise to lock different types of feeds.
If you really want to know what it takes, download this spreadsheet which is useful to compare the measured C/N versus the known parameters a certain feed is using, you can then determine exactly how much margin you have in your system for that feed.
Personally I think something was wrong with that transponder the other nite. I'll try and check it out again later tonite, see if it still acts up on me here.
If it does there may not be anything really wrong on ur end.