I had to add a feature holder between the XML templater and the HTTP Caller.

Seems like only part of the solution though.

do you have any reverse proxy/firewall/load balancer that may have size restrictions on calls causing it to be blocked on server?

That was a good suggestion. That got me thinking in a new direction. The throughput for the job doesn't exceed the limit on the network. However, I did scale back concurrency and rate limit. That did help so maybe there is an app limit for throughput. I still have to use the feature holder between the xmltemplater and the HTTP caller. Unsure why. It seems like its trying to make the call before the templater is done? Anyways with the feature holder, concurrency limit and throwing in an attribute keeper to limit data to the last HTTP transformer], things seem to be working now.