TCP Out of Order packets

We have sites that homed to the hub for resources and users are experiencing slowness. Captured traffic on both end hosts and receiver is getting lots of out of order packets based on the Wireshark analysis. However, UDP traffic such as VTC is not affected. Captured the UDP traffic from both ends and the IP ID numbers all matched. From info provided from the network group, no load balancer is in place, routing, LAN and QOS checks out. There is firewall used in the network and traffic is GRE. Not sure why TCP traffic is affected and not UDP.