It's 1998 on the BB server, and after playing this game for god knows how long I should be able to make this work. But I can't, and the in-game help and a forum search (seltrac, retb ...) didn't get me anywhere. I feel stupid now.
There's the Signalling centre, RETB, TV, Signalling (Large) and Seltrac. With the Signalling centre I can see only the RETB stop board as a signal, and my trains don't go faster than 135 km/h if they go at all.
I have removed all other signals except for one-way signs, and checked with the ":" tool (display signals and directions).
There are RETB stop boards at both ends, and some for good measure in-between.
What am I missing?
The signaling centre should also provide (colour light) track circuit block signals. It does for me, anyway. Meanwhile the RETB control cabin only provides RETB signals. So I'd guess RETB is just not the signal type you want. Radio-electric or not, token block is mostly useful for single-track sections only used by one train at a time, where it allows only using the one signal regardless of any stations.
Also, RETB does indeed seem to be limited to 135 km/h, which is lower than the 160 of earlier forms of token block.