Adding 10Gbps interfaces slowed tcp traffic

[mouthpiec]

Hi,
We have a network made up of 6850 switches, and due to capacity planning the links between the Core Layers were upgraded from 1gbps to 10gbps interfaces (no other config changes were made). All other interfaces in the network are made up of 2x 1gbps with lacp, hence the bottle neck were the links upgraded from 1gb to 10gb.

The issue is the following... Once the links were upgraded it was noticed a sharp decline in tcp speed (udp is fine). Any idea what need to be done on the switches? When reverting back issue dissappears.

Thanks in advance