Sted:
Sorry to hear of this news. By "T-3" I assume that the pathology at surgery indicated some factor outside the prostate gland itself. This is highly suspicious as a source of your current psa. It appears you may not have a clinical recurrence because your psa never went to zero, though it was close. Pathologic G-6 is a sign that the disease may remain loco-regional. Treatment before psa reaches 1.0 is recommended, and generally the lower the psa the better. This translates to sooner rather than later. A consultation with a radiologist and oncologist is highly recommended. A urologist is now out of the picture as his work is done at this point, unless you have other uro issues that need attention.
Some men have success slowing their disease with diet, supplements and lifestyle changes. With a doubling time crudely calculated as ~14 months, this could also be of benefit to you, though I would not suggest this as an alternative to salvage therapy, only as an additional consideration.
I am not aware of HIFU (Ablatherm) used for post surgery recurrence, unless there is a specific target that can be identified with imaging. If your recurrence is microscopic, unable to be seen with any technology and recognized with psa alone, some type of conventional radiation rather than ultrasound will be your option.