sounds like you blew up. I don't perscribe to those (do X at Y time) nutrition plans. I do 1/2 IM's and its a lot by feel. yes, I know what works, but you have to be able to adjust.
Losing 4 MPH is what sapped the legs. the best thing to do (for me) is spend the first 10 miles or so slowly creeping up. Miles 10-53ish is the meat of the race. I put time on the rest of the MOP on the bike, knowing on the run, I suck.
The same is true on the run. First mile is getting used to the movements, 2-5ish ramping up, 5-13 the go time.
For me, its swim, hammer, jog/survive