Read Serial On Change - Firefly or Other method

Have been playing with Firefly's generic serial connection tool. Works pretty well but...

When I connect to an arduino that is outputting multiple lines of data in one shot, it is hit or miss catching them all. For example, if there are 20 lines of values I see all twenty lines much of the time but may only catch 10 or 15 other times. Is there a way to make this more reliable. Was thinking driven by some other event than my 5ms (have tried a large range of values) GH timer events. I want to get the data reliably and only once.