You need to create 3 new PIDs as follows in the format of "Long Name", "Short Name", PID, Equation:
Intake Air Temp 2 IAT2 2203ca (A-40)*1.8+32
Ambient Temp Ambient Temp [46]*1.8+32
Ambient to IAT2 Temp Diff (VAL{Intake Air Temp 2})-(VAL{Ambient Temp})
Then add the gauge Ambient to IAT2 and that should get you the total "heatsoak"...The trick to the third gauge is that there isn't a PID...you leave it blank and then create an equation referencing the first two PIDs you created.
Hope that helps?