I have tried posting this message 3 times. The administrator says he does not know why it will not post. He said to resend it. I am retyping everything to see if I included some unsupported characters...
The OP said "There is a second Jake Brake, HiLo switch, and it works fine,". Just because he then said "I generally only use the second Jake Brake when I am below 40mph" did not imply he thought he had two Jake Brakes. Granted he could have said the second Jake Brake position... low or only three cylinders.
It was obvious he had a true Jake Brake because of the HI/low switch as a exhaust brake is either on or off... no hi/low.