printing IPDS through a vpn issues

A long lost customer has called - they moved their i server to a data
center, with a vpn back to the office.

They do heavy printing on Lexmark's with IPDS, plus a dozen HP LaserJets.

Problem so far only in the Lexmarks.

Spools have hundreds of pages to print in duplex.

When the paper runs out, often the system doesn't know it and there is no
message qsysopr queue.

When paper loaded up, the printer sometimes has reprinted many pages,
possible from the begin of the spool (after

Taking the PAGE response (when there is a message)

Never had this problem when all was local lan.

Network admin claims no traffic is blocked,,,

I've read the IBM docs on message PQT3601 and other similar messages.

Has anyone encountered this issue and resolved it with any particular
settings.

I've followed several IBM recommends but still an issue.

These are not giant printers - in the 30 pages per minute range.

V7r3 and QSPL has always had additional memory allocated.

Printers are set to not timeout.

Jim