I have the exact same problem as the OP Mirciulikkk.

Using a Cisco EPC 2425 router since last Friday. Before that I was using a Atlanta Scientific router which worked perfectly for mIRC. Both are cable modems installed by cable company.

Nothing on the PC was changed in the changeover of routers to cause the problem. Relevant ports 113 and 6660-6669 are forwarded. Router manual is not on portforward.com either.

Now when i connect to any server on any network I do get the following for example(with local host/ip info cleared in options/connect). This connects quickly but it picks up the IRC server hostname/IP as my real hostname/IP!!
------------------------------------------------------------
* Connecting to helsinki.fi.eu.Undernet.org (6669)
-
-helsinki.fi.eu.Undernet.org- *** Looking up your hostname
-
-helsinki.fi.eu.Undernet.org- *** Checking Ident
-
-helsinki.fi.eu.Undernet.org- *** Couldn't look up your hostname
-
* Identd request from 195.197.175.21
* Identd replied: 60953, 6669 : USERID : UNIX : ppgurra
-
-helsinki.fi.eu.Undernet.org- *** Got ident response
-
Welcome to the UnderNet IRC Network via Wippies, ppgurra

End of /MOTD command.
-
-Helsinki.FI.EU.Undernet.org- on 1 ca 1(4) ft 10(10)
-
Local host: irc2.saunalahti.fi (195.197.175.21)
-----------------------------------------------------------

Then I am unable to do any commands like /whois ppgurra or join a channel as nothing happens when I enter them. After a short while i do get the usual 'software caused connection abort'

----------------------------------------------------------------
Local host: irc2.saunalahti.fi (195.197.175.21)
-
* [10053] Software caused connection abort
-
* Disconnected
-
* Connect retry #1 helsinki.fi.eu.Undernet.org (6669)
-
-helsinki.fi.eu.Undernet.org- *** Looking up your hostname
----------------------------------------------------------------

After the software abort, the nick is just left on the server for a few minutes before timing out like a severe lag.

Debug window:
----------------------------------------------------------------

-> helsinki.fi.eu.Undernet.org NICK ppgurra
-> helsinki.fi.eu.Undernet.org USER ppgurra "hotmail.com" "helsinki.fi.eu.Undernet.org" :ppgurra
<- NOTICE AUTH :*** Looking up your hostname
<- NOTICE AUTH :*** Checking Ident
<- NOTICE AUTH :*** Couldn't look up your hostname
<- PING :3167564465
-> helsinki.fi.eu.Undernet.org PONG :3167564465
<- NOTICE AUTH :*** Got ident response
<- :Helsinki.FI.EU.Undernet.org 001 ppgurra :Welcome to the UnderNet IRC Network via Wippies, ppgurra
-> Helsinki.FI.EU.Undernet.org USERHOST ppgurra
<- :Helsinki.FI.EU.Undernet.org 002 ppgurra :Your host is Helsinki.FI.EU.Undernet.org, running version u2.10.12.12(2)
<- :Helsinki.FI.EU.Undernet.org 376 ppgurra :End of /MOTD command.
<- :Helsinki.FI.EU.Undernet.org NOTICE ppgurra :on 2 ca 1(4) ft 10(10) tr
<- :Helsinki.FI.EU.Undernet.org 302 ppgurra :ppgurra=+ppgurra@195.197.175.21
-> Helsinki.FI.EU.Undernet.org MODE ppgurra +i
-> Helsinki.FI.EU.Undernet.org WHOIS ppgurra
-> Helsinki.FI.EU.Undernet.org JOIN #help
-> helsinki.fi.eu.Undernet.org NICK ppgurra
-> helsinki.fi.eu.Undernet.org USER ppgurra "hotmail.com" "helsinki.fi.eu.Undernet.org" :ppgurra
<- NOTICE AUTH :*** Looking up your hostname
<- NOTICE AUTH :*** Checking Ident
<- NOTICE AUTH :*** Couldn't look up your hostname
------------------------------------------------------------
I've been on IRC for many years and never had this problem before. Out of maybe 50 attempts at connecting, 1 or 2 will get through without the lag but still with the wrong IP/hostname.
Its the same issue with Xchat, IceChat and hIRC so I think suspicions are towards the router.

Also, i found the following on the web. Would it be a packet problem?
post 18 about filtering IRC packets
http://www.boards.ie/vbulletin/showthread.php?p=62796755