Hey David,
Your coin is Trebonius Gallus from
Viminacium as noted. There are a lot of different
legend variations/ errors for this period at
Viminacium. Your coin appears to read
IMP C GALLVS P
FELIX AV with the
reverse PMS -
COL VI / ANXIV. This appears to be a variant of
Martin 5.21 which is not listed.
Martin 5.21.7 would be a match to your coin except the given
obverse legend ends AG instead of AV.
Martin 5.12.13 would be a match if your
exergue reads ANXIII instead of ANXIV. I can't tell well enough from the photo, but you may be able in hand.
Kurt