I was fully synced but it slowly falls behind of other nodes block count.
This can happen if the network is under heavy traffic and is most likely a hardware or network issue of your node. Minimum recommended hardware is 2 core CPU, 2GB ram, a good SSD drive and a decent network of at least 10Mbit/s. Please make sure you meet those specs and also that you run latest node version. A powerful node would run on a dedicated server with 4 cores, 8GB ram and 100Mbit/s dedicated network.
If it consistently struggles to keep up even at low traffic please let us know and we can look further into the issue. You can check current nano transaction traffic here.