Chris. When working as a mechanic, I once had the displeasure of a Nissan fwd auto that had a seized lock up clutch in the converter. Would do the same, idle ok until it was put into gear - it would then stall. What I'd do to isolate the the torque converter as the cause would be to run the car on stands as you've been doing. With the tran's in drive and wheels turning, slowly put the brakes on and view the rpm on the tacho whilst listening to the engine note for any load changes. If the converter's locked up you should be able to force the engine down 400 to 500 rpm, just as u can with a manual gearbox. It may even go below that, much to the engine's disgust. If it goes just below 800 rpm and thens stalls without any warning, then look elsewhere. The guys above me seem to know what activates the t/c clutch which is great, but won't fix the prob' if the t/c clutch has seized. So once all the checks have been done as suggested by me and the other genrtlemen, then it would be safe to say yes, the torque converter is defective. Hope I was of some help, Rob.