The problem isn't with your server (maybe).
The faster your character is, the more you notice higher latency.
etc, with 100 ms ping, you couldn't notice it walking around as a level 8, because your character is so slow.
But at lvl 200, running like a train, you'll notice the higher latency a lot more easy.
If it's "lagg", it's because higher latency which is a lot more noticeable at high speeds.
If it's "laggy walking, but not lagging game" it's because a speed mismatch in C++, your source tell them game the speed of character, and tell the client something else.
A missmatch is heavily noticed if the difference is only 0.05 ms in walkdelay (only at higher speeds).