There were very few changes to the core search routines between 7.2 and 7.5 so I imagine the problem is a change in configuration, e.g. where you using caching before, or a change in the types of files searched, e.g. PDF, TXT?
Can you provide a little more information on what types of files you're searching?
I'd also recommend raising a support request via the Generate Error Report option on the Help menu so your configuration can be viewed by support.