Make sure you do a clean install to remove any non Tiger compatible components that may remain from pre 6.9.2 versions (if appropriate). 7.3 and 7.4 are full installers that do not need a prior version to be present on the system.
I have read reports that installing in stages can help. That is, install PT but uncheck plug-ins etc. Repeat the process installing one component at a time.
I take it you've got plenty of spare HD capacity on your system drive?
I have an almost identical set-up and I've never seen this problem though I have not upgraded beyond 7.3.1cs7.
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