I'm wondering if it isn't time to eat crow. I'm starting to think if you are using the LT-20 you may need the Delorme Serial Emulator in the mix, which is the exact opposite of what I stated earlier. Keep in mind that my GPS receiver is the Delorme BT-20 and connects via Bluetooth. My setup works fine without the Delorme Serial Emulator, so at this point I'm not sure whether you need it or not when using a USB unit, but since it's labeled as a driver it may be necessary. I'm going to keep researching this topic to try and come to a conclusion.
In the meantime, if someone on this forum uses an LT-20 and shares it amongst the others apps mentioned, it would be nice if they would chime in to offer some solutions.