Every converter is a 'stall' converter, some stall at higher speeds than others. Your original stock converter is a 'stall' converter designed complement the stock motor. If you have a 700R4 it will lock the converter in OD, and this negates any slip in the converter, resulting in a 2500 stall converter acting exactly like the stock one. One thing to consider when running a 700R4 is exactly what you described, they like to drop into overdrive at low rpm's, so your engine needs to be relatively efficient at those rpm's.
Here are some good tech Q&A sites for converters, especialy ones for 700R4's: