I don't know why John would rather have switches instead of pressure switches because that is a PITA to keep up with. I will say you can't just use those little switches like PATC sells, at least I wouldn't. I used two adjustable Hobbs switches, one low and one high with two relays wired so while the low pressure switch closes it doesn't activate the relay until the high pressure switch activates the high switch relay. The high switch relay is then latched to the low switch relay so it stays locked until the low pressure switch is released. Kind of confusing I know and I would have to dig up the schematic again myself to redo it but it locks up at about 46-47 and unlocks at about 42-44 MPH. Otherwise it will hunt between lock and unlock at the pressure switch setting.
I ran the whole deal through the O/D circuit in the PCM so I wouldn't get lockup without it being in O/D and used a third relay in that circuit so I wouldn't burn the driver out in the PCM. Works like factory, really.