As I get all the bugs worked out of my '94 LeSabre, I've noticed that the transmission makes a clunking noise on the 1st to 2nd gear shift, but ONLY when the car hasn't been driven for several hours or overnight, and only on the FIRST shift. If I stop the car and accelerate after it has already made the 1st-2nd gear shift, there is no noise. The noise happens just after the car shifts, not precisely in time with the shift.

The car has 82k miles.

This car was driven very little for ~5 years. Might something have gummed up? I'm thinking I should get the fluid and filter changed as a first step.

Thanks,
David

Definately check the fluid. If problem persists, then it is something else :)

Try changing the fluid and filter. Sometimes this will cure your problem.
Another cause can be a faulty shift solenoid. This is an internal item and should be checked and repaired by someone familiar with trannies and their operation.