You need your SLT's to have their T/R connected AHEAD of the line card, not behind it.
Otherwise, there MUST be a slight delay between when the A leads open/close as opposed to the T/R switch hook leads. It looks like your circuit design causes the T/R and A lead closures to occur at the same time, which will never work with your SLT's T/R connected on the station side of the line card.
