At least Denton now has the A Train that along with DART and the TRE can get you to Fort Worth to catch the Texas Eagle or Heartland Flyer.
Except that it's a terribly long and inefficient way to travel. You'd have to take the 3.00pm A-Train out of Denton get off at Trinity Mills at 3.32pm, transfer to DART Green line train departing at 3.41pm reaching Victory station at 4.16pm, transfer to TRE departing at 4.25pm, reaching FTW Amtrak station at 5.14pm and then
finally board the Heartland Flyer departing at 5.25pm, reaching OKC at 9.39pm. Congratulations! You just did a 6 hour 39 minute journey for a distance that can be driven by car in 2 hr 30 min.. in other words,
you can drive from Denton to Oklahoma City in the amount of time it takes to take the trains from Denton to Fort Worth to board the Heartland Flyer!