I too would be surprised if the collar was malfunctioning. Stephen, this is extremely important. The collar must be very snug on the neck. If it is not the collar will give the dog stimulation sometimes and not others, which causes complete confusion in the dog.
IT IS NOT NORMAL FOR THE DOG TO RESPOND TO THE COLLAR IN THE WAY YOU DESCRIBE IN YOUR EMAIL.. I what I fear is happening is that you have trained in the compulsion method of training and the dog's true understanding of the commands is not clear. It also sounds like the stimulation level you are using is too high.
If you can say the word without the correction collar on and the dog responds without any physical directive from you, then and only then does the dog understand the command.
Therefore, my recommendation is to step back in training. I believe your dog is shutting down mentally, because he just is not sure what to do. If you force this dog, a couple of things can happen, one, he shuts down even further, reacts aggressively, or complies but is not learning thru the process.
The Tri Tronics collar jumps from one level to the next in severity too quickly for me, that's why I use the Dogtra.
I believe the dog is a soft dog and the collar level you are working on is just too much for his drive level.
SOOOOOOOO.
I would put all your collars back on.
Make sure the collar is snug.
Go play in the yard with him.
Repeat for a number of sessions, very short time periods and at least 6 different sessions.
Make sure you are playing with him on a long line so that you hold the line is not cuing him.
You need to have some tasty treats or his toys, whatever he likes the best. You will be using either of these to pull his mind back into you after you've used compulsion to get him to do a command.
PLEASE work at a very low level on the collar and nick the collar at the same time that you give direction on a flat collar.
For example, if you put him in a down, slight downward pressure on the collar with nicking collar in 1 2 3 cadence. Don't hook the leash to the pinch, just to the buckle. This will help the dog get over the mass state of confusion he is in.
I DON'T BELIEVE IT IS IN THE BEST INTEREST OF THE DOG NOR YOUR RELATIONSHIP to train using compulsion, or what some people call correction based training. The above advice is based on your description of your training method and how correction based trainers use the e-collar.
If......you want a better relationship and a more reliable dog I would purchase Michael Ellis' Marker Training Videos, Using Food and Using the Tug. It will open a new world to you.
I train differently with my clients and the ecollar, pairing marker training with the collar. It creates outstanding results, but I tried to answer your question the way you asked.
I hope this helps.
Roni