Regarding the series III it can be a tricky installation. We avoided it by going with a late series II PCM and converting to a cable operated TB with an LS1 MAF sensor.
Two different ETC systems aree used today. One is "torque follower" (the current version of ETC) the other is pedal follower that is an earlier version. The 3800SC series III is torque follower and very sensitive to the slightest engine modifications. Therefore new engine calibrations must be done for a Torque based ETC to work properly. Modifying the engines exhaust, or adding accesories to increase power changes the relationship between engine power and and throttle position. Torque based ETC systems often recognise extra power as a fault and will trigger "limp home" mode if the change is larger than about 5%. Also transmisson controls also affect torque output so again be prepared for a more complex PCM reprogramming if you chose to go drive by wire. It's been done before but it is harder than a series II swap.
