As most on here know, I've had mine for 4 years. As per my sig, I tow 15K and would not want to tow without it. The price is steep, but the results are for sure. The split between gears is about 600 RPMs. And on the five speed that is a very good thing. You will have to get used the shifting, but the operation and the ruggedness of the unit is unparalled. I don't know the 6 speed 5600 so can't comment on the necessity of the unit on that transmission. If the splits are right you shouldn't need the splitter, but I don't know.
Best of luck.
. . Preston. .