GPT partitions missing, upgrading 7.4 to 8.3

[Nicola Tiling]

Hi

I'm trying to upgrade 7.4 to 8.3, but I fail.

On a third slice I have nine gpt partitions. Originally they were created under 6.2 with "gpt".  The upgrade from 6.4 to 7.4 runs without problems, but now from 7.4 to 8.3 the partitions are not found. I can't see them under /dev and gpart list shows curious things, a fifth slice in the third and a EBR scheme instead of GPT.  
I have load the kernel modules geom_part_gtp, geom_part_mbr, geom_part_bsd. Is there a save way to install 8.3 or is it dead-end?

gpart list - 8.3
=======================

Geom name: da0s3
modified: false
state: OK
fwheads: 255
fwsectors: 63
last: 894563459
first: 0
entries: 14199420
scheme: EBR
Providers:
1. Name: da0s5
Mediasize: 458016491008 (426G)
Sectorsize: 512
Mode: r0w0e0
rawtype: 238
length: 458016491008
offset: 512
type: !238
index: 1
end: 894563459
start: 0
Consumers:
1. Name: da0s3
Mediasize: 458016491520 (426G)
Sectorsize: 512
Mode: r0w0e0


gpart list -  7.4:
=========================

Geom name: da0s3
fwheads: 255
fwsectors: 63
last: 894563426
first: 34
entries: 128
scheme: GPT
Providers:
1. Name: da0s3p1
Mediasize: 3172244992 (3G)
...
2. Name: da0s3p2
Mediasize: 107374182400 (100G)
...
Consumers:
1. Name: da0s3
Mediasize: 458016491520 (426G)
Sectorsize: 512
Mode: r9w9e18