The problem is not the ALDL cable, or even necessarily the USB to serial cable, it's the way Windoze enumerates the port, and sets com speed (baud rates). The PC is looking for a certain rate of data exchange. With the non-standard buad rate of the GM ECM, trying to communicate with the USB to serial converter, sometimes packets get missed in either direction, and a loss of communication happens.
The only way to almost guarantee that the ALDL cable you have works is usually to buy a very expensive USB to serial adapter, which will be almost as much if not as much as buying a new USB ALDL cable.
There are other ways, as Robert is suggesting, to find specific converter chips, that you may be able to find at cheaper prices, but then you still have extra connections, as in the adapters, the power port plug, etc.
I am also part of the group that tried to make a serial ALDL cable work with a USB converter, without success. I made a MAX232 based ALDL cable years ago, that works with any native serial connection, in fact I still use it frequently with my test bench, since my desktop PCs have had native serial connections for a while now, or through the use of a PCI serial card. I gave up pretty quickly, and just bought the moates ALDL Xtreme about 8 years ago, and have never had an issue with it. I have used it on MANY cars over the years without issue, at least no issues that weren't user created. ;)
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