The first generation of the GTX was from 1967 to 1970. The suspension on these cars was incredible for a muscle car of this type, which really set it apart from other cars in its class. The base engine was the Super Commando 440, a very powerful engine that made 375 horsepower. That was pretty good, but some customers wanted a little more. Plymouth was happy to oblige them with the 426 Hemi. That particular engine was lighter than the 440 and made an amazing 425 horsepower. Just over 700 were bought with that engine option, but you can be sure that they are in VERY high demand today. First generation models were sold as 2 door convertibles or hardtops. The convertible with the Hemi in good condition sells for six figures.
Sales on these cars lagged for a variety of reasons, price being the major one, and design being another. For some reason nobody seemed to like the way these cars looked.
In 1971 the GTX would be its own model for the final year. The 426 Hemi was still an engine option, but the more-than-capable 440 remained the more popular choice.
It was now sold as the 440 four barrel or the 440 w/ three two barrels. The latter made 385 horsepower. The redesign was quite dramatic for this year. The front grille was given a quirky chrome outlining with no apparent screen in the center. It was similar to the 1968 and 1969 Dodge Chargers, but with a less squared grille appearance.
For 1972 through 1974 the GTX would only be sold as an option on the RoadRunner.
I've been told that this car was driven by the main character on a WB show called "Angel." It was a 1967 model. My research shows that it was a Joss Whedon-directed TV show, so I'm sure it was probably horrible but has a lot of fanboys (and girls) who will not be happy with my criticism. I'll say this: the main character drove a cool car.
These cars are very collectible, especially those with the Hemi engine. For less expensive models, try looking on the eBay listings. Even without the Hemi, the 440 engine was still very powerful and with the tuned suspension and upscale options this is definitely a decent choice for anyone looking to buy a muscle car.