Gosh, John, are you sure you're not handling my dog! This is familiar territory for me.
I have a 5 year old who is very talented and can do the work but becomes an “Indy” during a test. (Actually, she tries to be an "Indy" during training, too.) I finally got a second Master pass on her after 2 years and many HT's!
Some of the things I’ve learned from smarter folks than I.
Don’t enter your dog in too many tests.
When you train, follow the EXACT same routine that you do during a test – from airing to exiting the crate, to walking to the blind, holding blinds – everything. You don’t have control over the crowds or excitement or number of other dogs at a HT – but do everything that you DO have control over.
Don’t rely on the collar too much if you think your dog is collar-wise. You can make it "up close and personal". We took the collar off my dog when doing marks and honoring (she’s a breaker) and I use the heeling stick or else take her down if she misbehaves. (and I’m middle-aged) Someone once told me that that’s why dogs have ears – not just for force fetch. By doing that, she seems to know that having the collar off does not mean she’s not going to get corrected when she makes the “wrong” choice.
In training, don’t accept anything but your dog making the right choices. If he chooses not to have good line manners walking out of the blind then drag him back and do it again and again until you get the behavior you want. I guess that’s attrition – where you just wear them down till they do the right thing.
Of course, they are living beings so nothing is perfect all the time, but I have seen an improvement in my “Indy” that I hope will enable her to get her MH before she retires!
Good luck!