Same here, even for a dual purpose car. Went from too tight to too loose to just right to finally improve the 60-ft and reign in the slippage on the big end. The difference between the last two converters was .2 and 2 MPH, all the result of reduced slippage.

Getting a carburetor that's "happy" with the rest of the combination has shown solid improvements, too. Doesn't have to be any bigger or make more HP if you can improve the shift recovery.