At startup with the G3 card, the onboard 603e CPU is doing all the work until the Sonnet extension loads. You'll note that the Sonnet extension will load first up, resulting in a much faster boot. If it isn't, you can rename the file with a 1 or something at the front so it is loaded first. I'm fairly sure the 603e CPU isn't "disabled" as such but still running, with no CPU load.

Does the Sonnet G3 make the faulty TAM work any better installed?

JB