I was running through the patches in my other GT-3 and I found that it also had a nice Univibe like rotary effect. I would postulate, that the GT-5-6-8 would have similar patches.
Better in a stereo setup though.
The effect might me COSM as the GT-3 is a COSM & analog Multieffects.
The slow speed on the dynacord CLS 22 rotary effect unit i have is more like a univibe with a bit of chorus than the opposite way that most other sims seem to be..all analog with a lovely warm sound,fast or slow..i can only surmise that some of the inventors of these type of units like the early uni vibe and the dynacord must of went with a slow speed of one particular type of leslie speaker that produced this sort of sound slow and some of the others ie..H&K,etc went with the classic phaser/chorus sound....one other strange thing i've found if you use the dynacord through a effects loop it goes more chorusy and straight through the front end of an amp you get a more uni vibe thing going on plus you get the classic fast leslie speed if you need it and it even ramps up and down like an original leslie and you can use it with a two way switcher off an amp for on/off and fast/slow.......the only thing is it's a rack effect and not a pedal.... i picked mine up for 280 euro secondhand as they haven't been made in a few years but were �760 sterling when they came out in the 80's...........