This is standard with Vetoryl/Trilostane. It is not a stable drug so it doesn't maintain control very well over time in most dogs. This is why it is so important 1) to know the signs of not only low cortisol but high and 2) to keep up the very sspecific testing schedule for this drug. The monitoring ACTHs are the only way to be sure the cortisol is once again elevated (and rule out other possibilities for the changes seen) so be sure to have that done before the vet increases the dose. Typically increases are no more than 25% of the current dose. Just a reminder....once the dose is increased the testing schedule starts all over at the 2 week mark.
I'm lazy today and haven't read back thru Kobe's thread so I apologize you have already given this info....has his skin been checked for Calcinosis cutis? This is usually diagnosed via a punch biopsy.
Let us know what the ACTH shows and how things are progressing for your sweet baby boy!
Hugs,
Leslie