Hey all, I'm a noobie on this forum and first wanted to say hey.

I bought a 2000 Bonneville completely stock about 3 years ago. I only had typiccal problems with it so far (manifold, ABS sensor) that were fixed under warranty. Now The car is out of warranty (60k miles) and the transmission starts acting wierd. It actually seems like it may be slipping but I'm not sure since I don't know what a slipping tranny feels like. It almost always happens in lower gears. It does it intermittently but when I pull out from a stop sign (or sometimes when I'm exiting a sharp corner) I'll give it some gas and the engine will rev up and the car starts moving a little and then there'* usually a clunk (a bang if I'm on the gas hard) in the tranny and then it starts going the way it should. I changed the transmission fluid and filter but to no avail. Same result.

Does this seem like the trans is slipping? I don't know any other way to describe the problem by typing. Did anyone else ever have this problem? Advice?

Yes..revving while in gear as you describe does sound like slipping.

What model of Bonneville do you have? SE, SLE, SSE, SSEi?

To start off warm the car up fully, run through all gears and then check the fluid level. Bring it to the top of the cross hatched area on the dipstick.

Do you regularly do burnouts or beat the car (ie. Changing from forward to reverse while still rolling?)

I have an SE. no, I never do burnouts with the car and never neutral drop the car or go from forward to reverse while moving. However, I bought the car used with under 20k on it and do not know the previous owner. i wouldn't think there could have been too much abuse to the car before I bought it but who knows.

I will try checking the fluid as you said but I am pretty sure I filled it correctly when I changed the fluid and filter.

Could a transmission shop diagnose the problem by driving the car?

It sounds like the level may be low and hopefully that is all.

A trans shop should be able to diagnose from driving it.

i agree with boosty
definately start by triple checking the tranny fluid level, then your next step would be to take it to a transmission qualified mechanic/shop where a roadtest, and sometimes a scantool too will give them a good idea of whats going on

Could be a faulty converter as well. Any DTC Codes?