I just added this:
(debug,Probing result: #<_current_tool>)
O120 IF [ #5400 EQ 99 ]
G53 G1 F[#<_TravelFeed>] Z[#<_TravelZ>] ; Move Z0 for traveling
G53 G0 X[#<_ProbeStandOffX>] Y[#<_ProbeStandOffY>] ; Move to probe stand-off position
ELSE
G53 G1 F[#<_TravelFeed>] Z[#<_TravelZ>]
G53 G1 F[#<_TravelFeed>] X[#<_ToolChangeX>] Y[#<_ToolChangeY>] ( Moves to tool setter for manual tool change )
O120 ENDIF
The message result was Probing result: 0.000000
I'm beginning to think, either I don't have access to the tool when entering M6 T(tool number), or there is a different way to do this.