school me on differences between Dart, GT, and GTS?

real simple way of looking at it is the first 2 digits of the vin. All darts will start off with L. The second digit is going to be the class type.
L = low - shoe box w/paint
M = medium - starting to look like trim
H = high - ok, now this is a car
P = Premium - holy crap, I got to polish all this?!
S = Special - a mixed bag

GTS is to a GT what a RT is to a SE challenger. In fact, most if not all Mopar's use these type on designation. Not sure about actual Chrysler or Imperials but probably the same.

If it is a true 68-9 GTS the 5th digit is going to be P=340, H-383 or M-440, the P code could also be a Dart "Swinger" the other 2 you don't want. So send them too me. =)