After a bit more digging online I found scans of two '98 German GT catalogues that specify the gold colour as 'atomic burst'.
All atomic colours (atomic burst, atomic grape, atomic rust etc.) seem to be exclusive to 1998 GTs which confirms my frame is that year, although I cannot find any reference of any 1998 Avalanches that were offered in the gold.
Is it possible that some '98 Avalanches were sprayed the gold in error, or possibly that the atomic colours were used on different GT models depending on country?