GPT looks valid. Diskutil sees empty disk

External 3 TB disk.

Stopped working after a power bump.

GPT reports as follows:

bash-3.2# gpt show /dev/disk6
       start        size  index  contents
           0           1         PMBR
           1           1         Pri GPT header
           2          32         Pri GPT table
          34           6         
          40      409600      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
      409640  2930266584      2  GPT part - 48465300-0000-11AA-AA11-00306543ECAC
  2930676224      262144         
  2930938368  2929332616      3  GPT part - 48465300-0000-11AA-AA11-00306543ECAC
  5860270984      262151         
  5860533135          32         Sec GPT table
  5860533167           1         Sec GPT header

This looks normal.

bash-3.2# diskutil repairDisk /dev/disk6
Nonexistent, unknown, or damaged partition map scheme
If you are sure this disk contains a (damaged) APM, MBR, or GPT partition map,
you can hereby try to repair it enough to be recognized as a map; another
"diskutil repairDisk /dev/disk6" might then be necessary for further repairs
Proceed? (y/N) y
Partition map repair complete; you might now want to repeat the
verifyDisk or repairDisk verbs to perform further checks and repairs

Repeating this makes no change.

DiskUtil reports as follows:

bash-3.2# diskutil list /dev/disk6 /dev/disk6    #:                   
TYPE NAME                    SIZE       IDENTIFIER    0:    *3.0 TB     disk6

I figured that it might be a bad PMBR. From all accounts, this is just an MBR with a non-bootable partition in it. I created an HFS disk on a USB stick, and copied the MBR (dd if=/dev/disk7 count=1 of=/dev/disk6) to the ailing disk.

I used R-Studio to scan the disk. R-Studio finds files and directories and such.

Ran TestDisk (separate command line disk utility) It's numbers agreed with GPT's.

I then used dd to make a backup of the first 34 blocks of the disk, and used gpt to destroy and recreate the partition table.

  604  gpt destroy /dev/disk6
  605  gpt create /dev/disk6
  606  gpt show /dev/disk6
  ...
  610  gpt add -b 40 -s 409600 -i 1 -t efi /dev/disk6
  611  gpt add -b 409640 -s 2930266584 -i 2 -t hfs /dev/disk6
  612  gpt add -b 2930938368  -s 2929332616 -i 3 -t hfs /dev/disk6
  613  gpt show /dev/disk6

No joy. I'm missing something here.