James provides a good article to check out for some more info on the problem.
An option, and I'm not sure if this is viable, would be to use Wireshark on the server that is having high retransmission rate. Then analyze the port that is being used for the retransmission traffic. Wireshark link: https://www.wireshark.org/
Your network team may have already done this or looked into it, but doing it yourself (if possible) could give you some helpful ammunition in leading them to the problem