can't boot 5.5 TB GPT disk

FreeBSD bigback.housenet.jrv 8.0-CURRENT FreeBSD 8.0-CURRENT #0 r190917:
Sat Apr 11 19:48:25 CDT 2009
james_at_bigback.housenet.jrv:/usr/obj/usr/src/sys/GENERIC  amd64

I can't boot a GPT partitioned 5.5 TB disc, where the UFS root partition
is near the end of the disk.  If I put another disk in the system and
mount root from the GPT disk the system runs fine.

The 5.5 TB disk is partitioned:

bigback# gpart show
=>         34  11718748093  ad6  GPT  (5.5T)
           34            6       - free -  (3.0K)
           40       409600    1  efi  (200M)
       409640  11634190128    2  !6a898cc3-1dd2-11b2-99a6-080020736631
(5.4T)
  11634599768          128    3  freebsd-boot  (64K)
  11634599896      4194304    4  freebsd-ufs  (2.0G)
  11638794200     33554432    5  freebsd-swap  (16G)
  11672348632      4194304    6  freebsd-ufs  (2.0G)
  11676542936     33554432    7  freebsd-ufs  (16G)
  11710097368      8388608    8  freebsd-ufs  (4.0G)
  11718485976       262151       - free -  (128M)

If I try to boot it (disk1 so pressing F5 here) it fails looking like
this (there is no UART available so this is typed from a pic, with typos):

F1   FreeBSD
F5   Drive 1

Default:   F1

BTX Loader 1.00 BTX version is 1.02
Consoles: internal video/keyboard
BIOS drive C: is disk0
BIOS drive D: is disk1
BIOS 630kb/3136864kB available memory

FreeBSD/i386 bootstrap loader, Revision 1.1
(james_at_bigback.housenet.jrv, Sat Apr 11 08:19:00 CDT 2009
\
can't load 'kernel'

Type '?' for a list of commands, 'help' for more details
OK

To get this far suggests to me that PMBR and GPTBOOT worked, and that
the problem is elsewhere.  Suggestions?  Could there be a 32-bit
truncation lurking in a loader somewhere?

PS. Note that the "lsdev' command causes the loader to crash while
printing out the info on the big disk, right after the EFI line for ad6p1...