software:
TunerPro and TunerPro RT - Professional Automobile Tuning Software i prefer V5, though if your computer can't support it, V4 will still work. then you'll need the ADX (V5) or ADS (V4) for your application, i can email or put them on a file server for you.
cable will depend on if you want to make a USB or serial version, depending on what your computer has. if you have the option, go USB, it's much simpler. the serial version would require a MAX232 circuit to convert the TTL signals to RS-232 specs so that the computer will play nicely. a USB version only requires a USB to TTL converter, which takes all of 2 wires to connect (i'll expand upon this later, if necessary).
yes, the stock temps are way too high... running a 195*F thermostat, i run either a 205 or 210 *F on temp for fan 1, depending on how sticky the thermostat tends to be. then slightly higher for fan 2. i rarely see/notice the fans on, but i never see the temp guage creep into uncomfortable territory.
i know all about 3100s and their tendacy to make noises implying immediate death... lifters and piston skirts are responsible for that, but i've had it happening for over 60,000 miles now and it still runs great otherwise.
since the odometer and speedo seem to be off by the same amount, i'd say the calibration is compromised due to GM not wanting to support another calibration.... so with your wheel/tire combo, it reads slightly too fast, but with another offered combo, it reads slightly too slow. not too big of a deal to compensate for, though if i were you, i would check the speedometer against what the ECM is commanding it to be in the datastream.
while the stock EPROM can be erased via UV, they're nearing their end-of-life date, so i replace them with EEPROMs that have a 100 year rating. that and 1.5 second erase times compared to ~10 minutes is a no-brainer.