One thing I haven't been very good at in the past is doing routine brick workouts. I had convinced myself that they weren't really that important, as I seem to run OK off the bike in sprint and olympic distance races. But, I'm 0-6 on running well in IM, and probably 0-4 in running well in half-IM. It's probably a combination of things that cause this, with the biggest one simply being that I'm riding a bit too hard. But, in every IM I've done I've felt horrible right from the beginning of the run even when I felt fine on the bike. So this year, I'm making an effort to do a short run after every one of my longish bike rides. My Sunday rides are up to 60 miles now, and I run 2-3 miles after finishing up. The runs are hard but not horrible. I hope it's helping.