In my experience Yes, therapy does work, I experienced therapy in my teens and found it very beneficial. My technique to avoid a block is not to word replace but tap it out.. in other words focus on what you are going to say then create a diversion by tapping your foot silently this always gives me a 100% success in avoiding the block and remaining fluent. Don’t try and swop words last second as that will always affect fluency. Hope my experience helps.