Should be no need to use double pulse or use longer than .8 duration for the lock pulse. Something must not be wired right if it works in one direction and not the other. I tapped into my lock/unlock wires behind the glove box in a wire harness on my 98. Mine didn't have factory keyless entry either if that might makes a difference.

A negative pulse to Red/Blue should lock

A negative pulse to Brown/Red should unlock

There are several places you could pick up these wires. Mine was already tapped behind the glovebox from a previous alarm install. The wires can also be found behind the radio close to the relays found there.