One needs to qualify which tall 5th they are referring to there's a 0.62, 0.642 and 0.655 all taller than the stock 0.705. IMO for highway cruising at the 70-80 mph speed the taller 5th makes a big difference, it was about $1500 to add while the box was apart for a rebuild if I recall.
If you have a stroker motor or a built engine with a lot of torque, you could swap to the 3.77 and a taller 5th.