I guess you have the 5 button DIC then, my 05' GTP has a 3 button so I installed a boost gauge to see what was going on. When you said your 8th digit is 4 that is the 3.8L SC engine I'm not sure where you got that info on a 4 cylinder it was never even an option on these cars (04+). The RPO codes are under the carpet in the trunk. As far as the temp gauge goes it's standard 100-260F (38-127C) gauge it just isn't marked. Typically the temp will run between the 1/4 mark and the center with it going a needles width over the center about the time the fans turn on (217F,103C) low speed.
Jeff