NEVER dethatch St Augustine unless you want to plant something new. Dethatchers will simply remove the entire lawn.

How often are you watering and for how long?
When were the last two times you fertilized and what did you use?

Your long cold winter is likely the problem. Now, how to recover? Answer the questions and we can get you on track.

I am going to hijack this a bit. I also am in the dfw area with same issue. there is growth but seems to be quite a bit of dormant/dead layer still there. should i go out there and try and rake up the dead/dormant stuff? putting down about 1" of water per sprinkler cycle every 5 to 7 days. used the calloways lawn food in early april when first started greening up. put 17 lbs down in approximately 2500 sf. those number might be a little off but i used the texag extension publications to calculate the amount. might have been a little soon