Getting to the gate depends on the airport. At DFW, security will probably not let you through unless you have a boarding/security document.
About a year ago I was in uniform trying to go through DFW. I went up the security gal (Not TSA). She asked me for my boarding pass. I told her I was a SW pilot and did not have one. She then dramatically puts her arms and legs out to block me from moving forward and tells me I need to go to the ticket counter.
I go over to the ticket counter and get in line. I am the line, no one was there. The CSA calls next and asked if I was listed. I said no. She says that she will do it for me but some of the others might not. I was the only one in the line!
The last time I used Delta. Their security let me through but it may of been a fluke. At SEA, my commuter airport, Delta is in our terminal.
Casual Business or Uniform attire.