After your long taxi and run up, did you switch tanks before departure?
Quite a few years ago I shared a Cherokee 160 with two other guys, one an experienced and capable pilot and the other a friend of his who was working on getting his PPL. After I sold them my interest in the plane they got another student to buy in who with an instructor crashed the plane off the end of the runway after taking off with the fuel shut off. What I was told was that the instructor had this goofy idea of doing the run up on the lowest tank and then switching to the fullest one for takeoff. To make matters worse the detents of the fuel valve were quite worn and this required one to look carefully at the handle position to make sure it was where you wanted it to be. Anyhow, the student inadvertently shut the fuel off when ready for takeoff and found that the carb held enough to just nicely get them airborne. I'm not suggesting this is what happened in the subject case but GM's post reminded me of this accident.