Are you pedalling in circles?

The bike is not a leg press machine! You need to pedal in circles, think less about pulling up, but more that you are trying to get the up stroke out of the way of the down stroke, think of your leg as a dead weight, the average leg is going to be a few kg in weight (each leg is on avg 10% of your total weight), that if you don't get it out of the way as quick as poss on the up stroke you're not just pushing down to propel the bike forward, but also to lift the dead weight that is your leg.

Not everyone has the benefit of a Watt bike or spin scan software, but next time you are on the turbo after your warm up for 20-30 sec do one legged drills (un clip shoe and rest on the turbo)on each side and see if you have a dead spot in your pedal stroke, normally it will be last part of the up stroke and just over the top, but also notice when you clip both shoes in how much freer and faster your pedal stroke is because you have switched on all the muscles in the pedal stroke.

If you don't have a turbo, you could possible do this on a quite bit of road (please be safe) find a bit of road with a very slight drag, un clip one shoe and hang down, pedal one legged and wake up all the muscles through the pedal stoke, do both sides then clip both shoes back in and carry on with your ride.

Try the above not just on the hoods but on the drops as well, if you have more of a dead spot on the drops then maybe the bars are too low/or bars are at the wrong angle and the hip flexer is too closed up that you are unable to get the leg over top dead centre, also try this on tribars of your tt bike. If you can't then maybe you need to raise your bars which will open your hip flexer allowing you to get over top dead centre or even your cranks are to long (will go into this later)

I understand more since I've started bike fitting why when we were younger we were taught to use low gears over the winter, when you spend a good chuck of the winter on 42-17 or 18 (some people used a lower gear) the up stroke becomes more of a reflex action, because if you don't get the up stroke out of the way quick enough you will bounce all over the saddle, so you learn to pedal fast and smooth and 'pedal in circles'.

Crank length, people think more about this in terms of leverage, yes it may help but too long a crank will close the hip up at the top of the stroke. At the bottom of the stroke your ideal leg extension will be no different if you use 180mm cranks or 165, but at the top of the stroke you will have closed the hip up a lot more with the 180 compared to the 165 cranks. With a shorter crank the other benefit is you can get lower and more aero because there is more room in the hip flexer area. This is also of benefit to triathletes, especially ironmen, the more open the hip flexer the easier the tradition from bike to run. Kona Ironman winner 2011 Craig Alexander (who is 180cm tall) used 167.5mm cranks for fastest bike split (I think!)