Another option is from SICO tools to buy a chinese tech 2. Even with shipping most are getting them delivered for around $300. Then you can do ANYTHING GM can do to any of the electronic 6.5 diesels or GM cars from around 91 up to 09(some later models can, but I believe 2012 is the cutoff for the tech 2). And before anybody says anything about them being chinese, no they're not perfect, do not try and update them with GM software(doesn't matter as GM hasn't released an update since 2012, and no future updates will ever be available), and they are known to have a few little quirks, but for the most part they work good(only real issue is with them shutting off when starting the vehicle because the internal power supply isn't hat good, and shuts off below 11.5 volts. This problem can be corrected with a new power supply. I believe they said for about $60 in parts and a few hours work, you can make them as good or better than a genuine OTC built one).
As to the adapter, that only works if your scan tool is capable of doing obd1. Many of those negative reviews are from people thinking that adapter will make any obd2 scanner read obd1. Well this is only half true. GM OBD1 plugs do not provide power, so you have to have a scanner that is internally powered, and your scanner must be able to read the data that is present at the obd1 plug. And not all obd1 plugs output the same data. There are several different data streams that GM used for obd1, so again it comes down to can your scanner do it, and does the adapter have the required resistors for some models. GMTDscantech is a very good option as well, and you can purchase a obd1 cable for $60 iirc to hook it up, or build your own.
