By the looks of it, Twisted Colossus' duel lift hills adjust speed to ensure that both trains hit the top of the lift hill at the same time regardless of when the operator dispatches the train. That's at least what it looks like in this video:
They never change speed, but the green lift is much slower. That is what everyone is saying who has ridden already (Source: TPR members). There are many POV's where the timing is off by the op which causes the train on the blue lift to either beat green to the top or be slacking behind green. It has been a big debate on TPR also to whether SFMM should be running it to duel or for highest capacity (which SFMM has said they are doing to increase capacity, rarely dueling).
It has to do with the rides sensors which tell ops if they can still make it duel if they dispatch at a certain time. No amount of sensors or systems in place will make up for SFMM operations though XD