I downloaded the full ZC 1.5.6 and pulled out the 1.04 versions of the firstdata_hco pages and ran them through BeyondCompare. Looked like there were some considerable changes, so uploaded the 1.04 versions.

Looks like it will now accept the 1K+ line items, and has accepted both a Visa and Master payment without error. Now need to double check to make sure it didn't double dip the card like it had before.

Thanks MC on the tip of the v1.04 in the new ZC build...I *think* we've got it now.