2:52 is a very solid time dude! Had a similar experience in my second . Was trying to get a BQ time and it was a little too hot and just not the right day. Instead of readjusting my goal accordingly I tried hang on to that pace like a noob is prone to do and the wheels fell off around 20. I think I was right on the edge of heat exhaustion , was seeing spots and stuff. So much of running them well is strategic and knowing exactly where that fine line between too much and to little effort it is and walking that tightrope between the two.