I have found it very useful to separate OD and lockup in my a-500. I have 1 switch that kills both and a second switch that will allow OD but not lockup. I have the vac. switch for kickdown as well as the adjustable pressure switches on the tranny to set the upshift speeds. IMO all of that is required to tune it to your vehicles needs and your tastes. I have 3.91's and 28" tires, I have it set to hit OD about 45mph and lockup at 55, those I very often keep lockup turned off unless I'm on the interstate. Even with 3.91's it tends to bog a bit, if I had 4.10's or def. 4.30/56's I'd let it sit up in lockup all the time (or if I had short tires)