Are you sure it is really slipping after lifting and then reapplying the accelerator? The reason I ask is, that at least on my 99 V6 Alero, the convertor unlocks anytime the throttle is closed, then when throttle is reapplyed it takes a few seconds for it to lock up again. But at no time is the trans actually slipping, since it would accelerate fine with more throttle opening.
Lee Richardson
Mech-Tech