Jumping with John - big wasn't better

On Sunday, Shannon and I went down for a jump lesson.  It started out superb - we had our distances, we were round, we had quick changes of lead.  Then John made the fences a little bigger, which usually helps us improve, but instead, this time, we just kind of fell apart.  Not completely apart, which was almost more infuriating.  We got really hit or miss - we'd either nail the fence and float perfectly over it - or totally screw it up (in any one of what felt like an endless number of ways).  And no matter how hard I tried, I could just not pull it all together to ride them all smoothly.  It was like fine - flop - fine - fine - flop - flop.
Bigger canter.  Which means more impulsion.  Which means quit digging in my heels so when I give an aid, Charlie leaps forward.  But this is where I'm hopelessly stuck.  If I give one aid - even with a whip smack - he goes back to dull.  That is probably because I have my legs glued on, but I can't feel it. 
Faster and more precise canter lead changes.  When I get overwhelmed, I give sloppy aids and we plunge onto the forehand and quite frequently go back on the wrong lead.  If I just take a breath and think - outside hand, inside leg, outside leg, it is going slower to go faster.
Sit up in between the fences.  Especially on a long line, start with the half halt and the rebalancing about half way between the two fences - not two strides out.  And mean it.
I know this is a lot better than last year - I can think of more things and feel like I have more time between the fences - I can feel the mistakes faster, and now a lot of the time I know what to do - I'm not always fast enough or effective enough, but at least I'm not completely ignorant.  But I am going crazy that I can't figure out my lower leg for impulsion. 
As Shannon pointed out, at the show she came up with a system that works - walk on a loose rein, ask for a trot, and if he doesn't spring into it, he gets three smacks with the whip.  Then ask for it again, and usually the next three or four requests, he springs forward into it.  So that fixes the start.
But how do I fix the anaconda cling around the whole course when I can't feel I'm doing it?  I got the pulling hands about a month ago when suddenly, in a eureka moment, I could feel I was pulling, and since then, I've been able to not pull.  So I'm just waiting for that eureka moment with my heels too.  But I'm ready for you, eureka moment - I'm ready to be done working on that and start working on the next thing.  I'm tired of Shannon and John having to tell me the same thing over and over and over again.  It's humiliating that I can't get that one thing right.