To be fair, you have an issue they cannot replicate making it very difficult to "fix" it.
The 58xx is in the Connectkey family, they all run identical code and there are "quite a lot" of locations worldwide that run them.
What you need to have done is to get a Wireshark trace between the printer and the PC to record all traffic between the two so that you can identify where the lag is. And since SNMP is disabled in the Printer and the PC, and 2 entirely different protocols have been used (LPR-RAW, which are ports 515 and 9100), the printer itself has been eliminated by submitting the job through CWIS.
So it is not the network, it isn't the protocol, it isn't the port, it isn't the job and it isn't the printer hardware or its firmware/software.
If you have spoken with 2nd level support in the last month there is no doubt the printer is running the Latest 072.190.145.05000 firmware and it was applied via the "Altboot no data backup, no clone" method as well. Which means there is no chance you have some odd bug in your system which makes it unlike any other printer.
If you are 100% certain you have an issue that is caused by Xerox code, have 2nd level page an onsite Analyst. They will come on site and find and resolve the issue and as long as the issue is not caused by something on the PC end it would be covered fully by contract.