I am training for IM Tulsa on May 31st and went to see what Best Bike Split said I should be able to ride this course at. After entering all my information and uploading the course it came back with a speed that was quite a bit higher than I was currently able to hit on my long ride (which at this point are still less than 3 hours). I figured this might have something to do with my wheels so I switch some old Hed Alps that were given to me for my Zipp 404 NSW's and went for a ride. This ride was better but still not up to where I'm predicted to be riding by around 2mph. I'm trying to figure out what else I should check that could be robbing me of this much speed. My bearings seems to be running smoothly. These wheels are only a few years old. I can't say how many miles I've put on them but when I've done some research I've found that bearings should last about 25K miles and I know I'm no where near that. My other thought was the bottom bracket. It's not making any grinding or knocking noises and was replaced about 5 years ago. I haven't spent a huge amount of time on my TT bike since then so I don't think that it's that either. Any other suggestions on what to take a look at would be greatly appreciated.

I've sent a video of my riding position to my coach for him to check and he agrees that someone putting out the watts that I am should be riding at the speed that BBS is predicting.