A stall converter, aka torque converter, is just a donut looking hydraulic fluid coupler that sits between the engine crankshaft and the transmission input shaft. Their job is to allow for slippage so that you can remain idling in gear when at a stop light, etc. and also depending on how the converter is set up, allows for slippage up until a certain rpm.
The stock converter on most overdrives are lock ups. Some aftermarket converters are not lock ups.
A stall converter can range in numerous rpms besides the 2800-3200 as you have heard. Depending on the pitch of the vanes to the output torque of the engine will depend on where and when a stall converter will stall. Some stall converters stall as low as 1600 rpm while others are 5000 rpm or more.
My big block Chevelle had a 3000 stall Hughes converter in it. It was required because I had a pretty big camshaft that required that size of a stall to make it work. (had I went with a smaller stall it would have been a real pooch off the line) I could cruise around town all day but as soon as I floored it, the stall allowed the engine to get into where it was really making power. The end result was a neck snapping tire roasting set up with **** loads of torque.
On a turbo Buick, a bigger stall is sometimes required with a turbo upgrade, depending on what size turbo you go with.
Hope this helps you.