The 'GFLink' field found only in the Import module links pay-cash gifts to pledges they pay. You can only export one 'GFLink' per pay-cash. A pay-cash gift can pay multiple pledges so you need to have multiple 'GFLink's per pay-cash gift. I would like the ability to export multiple 'GFLink' fields per gift. Another solution would be to add the 'GFLink' field to the export module.