70, Happy to hear I am not the only one who gets the blues on these projects, a nice thing is you can drive yours right now. As for the USB attenuation is 5 meters or roughly blow 20 feet. And, dasiy-chaining them will decrease the range, not like Claymore's and other pyro, your Signals guy would be smacking you. Also, sounds like the laptop is questionable as well, 2.0 to 3.0 needs to be in the architecture, so make sure you have 3.0 system, cables etc. They are reverse compatible down meaning a 3.0 can use a 2.0 cable but you may have issues the other way. I am assuming you are using a USB to RS-232 connection, seems the way many of the EFI systems are, so you have to daisy-chain. This gets sketchy, I know I didn't help in this babble, the point is sounds like your Point #2 (ECU Connection) may be a culprit, so take some time to validate it or it may be the ECU?.
Good luck, if I can help PM - I am solid lurker on the weekends, usually out on weekdays.
Charles