Fusion Drive High Sierra to Mojave Slow-w-w-w now

[steveonmac]

Hi, I upgraded my iMac from High Sierra (HFS+) to Mojave (APFS). Now it’s so slow it’s unusable. Right now, I’ve booted from an external drive with High Sierra. Anyone comment on where to go from here? My specs: Fusion drive iMac "Core i7" 3.5 27" (Late 2013) Identifier 14,2. Thanks.
/dev/disk0 (internal, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *121.3 GB disk0
1: EFI EFI 209.7 MB disk0s1
2: Apple_APFS Container disk3 121.1 GB disk0s2

/dev/disk1 (external, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *5.0 TB disk1
1: EFI EFI 209.7 MB disk1s1
2: Apple_HFS 2 - LACIE 5 TB EXT 5.0 TB disk1s2

/dev/disk2 (internal, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *3.0 TB disk2
1: EFI EFI 209.7 MB disk2s1
2: Apple_APFS Container disk3 3.0 TB disk2s2

/dev/disk3 (synthesized):
#: TYPE NAME SIZE IDENTIFIER
0: APFS Container Scheme - +3.1 TB disk3
Physical Stores disk0s2, disk2s2
1: APFS Volume HARD DRIVE 2.2 TB disk3s1
2: APFS Volume Preboot 45.0 MB disk3s2
3: APFS Volume Recovery 510.4 MB disk3s3
4: APFS Volume VM 2.1 GB disk3s4