Why is domain lookup and domainchecker so slow?
With the domain suggestion feature from WHMCS v6, domain lookup will slow down drastically if you select too much domain extensions for lookup.
Domain suggestion for hundreds of domain extensions does really not make any sense and will extremely slow down the required whois or availability lookup.
In order to speed up the domainchecker, only select a few tlds for suggestion.
Goto Setup -> General Settings -> TAB "Domains" and click "Domain Lookup" Standard whois -> Configure button
De-select all TLDs and save the changes
Do some domain searches to see the difference.
You can then later again select some tlds but you should not select too much tlds at once as it will slow down the domain lookup results.