my friend and I have been trying to play together for a while, we can join each others lobby's but when in game who ever is the non-host has about a 1-10 sec desync, we have tried restarting our games and it is not our internet.
#Latency issues
drifting tendon
gray jetty
Unfortunetely this is very likely about your internet. GTFO is p2p and the direct connect between you and your friend is likely very unstable and has a lot of packet loss (which is the primary reason of desync)
If one of you is using VPN, turn if off or try another node. Other than that nothing much you can do