Low-speed "clunk" 1-2 shift, A-904

OK, all this talk is great, but most of it is just flying over my head. Does anyone know where I can find an article that explains the basic workings of a Torqueflite automatic transmission?

Just to give some more details, it acts fine when putting into gear and never misses a shift or slips. The shifts are also pretty firm and quick at WOT. The only issue I have with this transmission is that when accelerating slowly and then gradually letting off the gas(forgot to add that part), for example when driving through a full parking lot with a stop at the end, it will most of the time "clunk" into second gear as I start to coast. If I am accelerating at a constant rate, no matter how slowly, it usually won't "clunk" like that.