Sounds like you might have a TC lockup solenoid going bad perhaps..Any other issues besides the dropout? Is this the first time this has happened? Check engine light come on or anything else when you experienced this? In fact, regardless of whether it threw a light, there may be a code stored in the PCM for the problem you had. I'd stop by an automotive shop & get them to scan for any codes first before replacing anything..
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1998 Pontiac Grand Prix GTP
F-Body Ft Brake Upgrade, CAI, Buick STB, 226k miles & counting, otherwise stock