What your touching on is probably my biggest challenge at the moment and your question might help solve the problem. Since doing 7730 conversion I have never had any success with getting my laptop to successfully communicate with the ECM using TunerPro. I've double checked wiring from the ECM to the ALDL plug and it all looks correct based on the pin-outs I have. I've always chalked it up to my lack of knowledge of setting up the proper BIN and ADX files. I always figured that so many others had done the same swap without any problems that it couldn't be a pinning issue. The last time I attempted to try TunerPro was last summer and I was finally able to see some readings but it was all garbled. For example the tach readings were all over the place even when the ignition was off. It could still be a setup issue I have with TunerPro, an incompatible ALDL cable, bad ECM or needing to re-pin the ECM with your information. It's to cold and we have to much snow at the moment but once it warms up I'll look into it some more.
I've been doing a lot of research on this topic, and my search had lead me to believe the problems with pulling data from the 7730 are switching-method related.
I don't know which cable you're using, but it seems that the "two transistor" type doesn't work well with some laptops. The "Max232" ic controller type seems to work properly with all types.
The data stream is not a stream at all. Opposite of the older, 160 baud data stream, the 81xx data is in packets and travels back and forth up and down the line, so in effect, instead of just "reading" data, you're trying to "communicate" with the ecm.
I hope this helps.
I haven't built my cable for the 7730 yet, but plan on just adding the second transistor to my existing one-switch setup and try it first, then build the Max232 rig if the other doesn't work.
Ron