The up and down slider thing, will give you more of one and less of the other (depending on which way you move it).
Sounds like The pins on Part #7 and the slots in parts #6 & 7 are worn. You may get by with adjusting #14 & 15 (keep in mind that a little goes a long way) remember to count your revolutions in case you want/need to put it back like it was.
http://www.partstree.com/parts/cub-c...sion-controls/
Check to make sure the "fork" on the sub-frame is properly positioned around the "footrest bar" under the tractor.
Look at parts #2 & 3 in Rolands exploded view, When lifted all the way up, they should almost touch the steering column cross-member. If they don't (usually the left side #2) then you probably have sheared spiral pin/s somewhere. Remember that the one on the right controls the one on the left, so either pin (or both) could be sheared. Don't attempt to replace them with a substitute pin or bolt of any kind. If those arms (parts #2 & 3) do go all the way up then there are problems elsewhere and may be a little harder to track down.
Good luck.