TweakMASTER does not affect the speed at which your dial-up modem connects to your ISP, whether that be 33,600, 42,000, 48,000, etc. That is negotiated between your modem and the modems of your ISP and only modem drivers provided by your ISP and occasionally initialization strings provided by your modem manufacturer will affect that connect speed in any way.
TweakMASTER, on the other hand, modifies the data throughput which you can achieve at the speed with which you connect. This varies according to many different factors, including general Internet congestion, phone lines, as well as the intermediary routers you encounter on the path to any Internet server you attempt to connect to. The trick is to try and optimize the average data transmission rates you can achieve while surfing the ’net.