Customs isn't the delay for me in the afternoon... it's TSA Precheck Security at D.... last time I only had 40 mins from landing to the next flight at A-16 and when I saw the huge TSA precheck lane and said "I'm missing my connection" a helpful agent told me to catch the terminal bus outside the terminal... I took that to A where there was no line and miraculously made my flight as they were closing the door. It was nerve wracking and I hope never to repeat it, but the terminal bus was not something I would have considered.