Are you seeing timeout issues in the logfile? If you are seeing something like "Timed out borrowing requestor from pool" then you just need to increase your pool size in the Service Package definition.
The end point URL used by the clients calling our services should go through normal load balancing unless you have something else configured there. Are the clients calling the service using a single node URL?
For REST and SOAP services defined in PRPC they should be available to run on all web nodes as traffic comes in using HTTP.