Pops out of first on deceleration only

[BUgsy71]

So my trans has started popping out of first, but only on deceleration.  It goes right back in, no problem.  Any ideas would be great.  New shift bushing, new coupler, shiftrod clamp and spring in place, new motor mounts.  Checked lockout plate, and clutch servo control arm.  I'm at a loss.