How to avoid packet drop

Hi All, I am running a tool that is a packet generator. With that tool i am able to achieve line/link rate on my 1Gbps network. I have two queries Query 1) When i run the same tool on 10Gbps network i am able to achieve only 5Gbps rate.( by network i mean i have two machines with Centos 6.4 connected back to back.) Query 2) When i run the packet generator on the 1Gbps link or 10Gbps link i see a packet drop by kernel ( result of tcpdump -i eth2).How can i minimize the packet drop? Thanks Clove