I get a good bang when i go off the line from a stop, I dont hear it, I just feel it. I can reproduce the problem by being in drive with the brakes on and pressing the gas at the same time, it will go "clunk" but you dont hear a clunk you feel it. Side to side its fine. Maybe this is normal? My 93 does not do it but its a different transmission.

Also when going into drive the car shudders decently from a similar "bang"...with the 4t65e should you feel it go into drive with a sizeable thud feeling in the car? My 93 with a fresh trans hits drive really hard too from park but it has a shift kit and vaccum modulator that increases the firmness in shifts etc. I guess I'm not sure how much is normal on the 00.

How does the fluid look and smell?

Yeah its a little burnt. I can get a pic..not terrible still red but not as red as my roomates 2000GTP..Maybe I need to drive that tonight to see if it has the same banging issues.

You aren't losing traction in either wheel when this happens right?

i would look into the motor and tranny mounts... sounds more like a mount problem im thinking... especially if you can get the result from powerbraking... does it occur during a heavy downshift as well?

Good point. I think the motor is moving too much just in neutral when you rev it....because the trans is completley solid in everyother fasion..shifts perfectly.

I'm going to detail the engine bay and check the mounts this weekend.

which ones should I be most concerned about? all of them? I plan on doing the front motor mount with the hockey puck mod.

by the sounds of it i would think that you should definately check all of them... the front mount is kinda soft to begin with on these cars, and a little movement is normal. You should definitely look into doing a soli hockey-puck front mount, but your tranny mounts may be shot as well

I would recommend changing your fluid and filter in addition to checking the mounts.

i might even consider checking the suspention mount points (ball joints, bushings, ect...)

I know its not suspension for sure....I can reproduce the problem by holding the brake down and pushing the gas rapidly to 2000 rpm or so.