MySQL DNS Lookup Delay - Internal IP

I have six dedicated servers on a VPR. I use one of these as the Database server and the other five connects to that server to read the Database.

When I setup my scripts for the first time I used the external IP to connect to the DB server. Everything worked perfect for these weeks:

mysql_connect('174.xxx.xxx.xx', 'user', 'pass');

Since three days ago I finally received the internal IPs of my servers and now I use the internal IP of the DB server:

mysql_connect('10.0.0.1:3306', 'user', 'pass');

When I did this last change this my database started to collapse. Queries stuck on a bottleneck every 10 minutes. Here's an example:

40468 simon 10.0.0.7:47002 pkindigo_db Query 115 Locked update `captured` set hp_left = '79', status = 'normal', att1pp = '25', att2pp = '30', att3p
40523 simon 10.0.0.2:58080 pkindigo_db Query 115 Locked update `captured` set experience = '5120', level = '16', hp_left = '58', hp = '58', status =
... (tons of locked queries before) ...

As you may see table is locked since 115 seconds for a simple update... after some hours this ends on a "#1135 - Can't create a new thread (errno 13); if you are not out of available memory, you can consult the manual for a possible OS-dependent bug" and even some of my tables finally crashing.

I think that my Database stuck because of a DNS lookup delay. When I had this problem before using the external IPs, I added skip-name-resolve and the problem was fixed. But now with the internal IPs it seems that's not enough.