G'day John Franklin.
Can i ask ,does the tractor have a selector valve under the seat,(front right hand side) usually it is a push pull arrangement with a knob on the end or a rotating lever with three positions, ie. rear ,straight up, and forward if it has try playing with the valve ,you may have knocked it when getting of/on the tractor .
The lever MoDeer43 has mentioned controls the rate at which the lift arms drop it does not control the rate of lift , the RESPONSE Lever it slides from slow to fast ,sometimes if the hydraulics have not been properly adjusted the response lever can if the SLOW position is selected STOP the hydraulics from going down simply move the lever towards FAST till you get the rate of drop you are happy with,it is a handy thing when you dont want the three point hitch to drop to fast and damage equipment so if you are as said using the tiller adjust the rate of drop till it goes down gently being mindfull that if you are using the DRAFT lever to control the depth ,if set to Slow the Tiller will be slow to respond .
If you are tilling land with different soil types and wet or dry I would suggest you use position control initially and say after two passes if you want to, use draft that will then work better it is just that the Draft control will not respond to different soil conditions and you will find that you are constantly messing with the Draft lever .
The more information you can give will make it easier to diagnose, like did you hit a tree root or a hidden rock anything that may have Shock loaded the linkage.
Happy Days.
Hutch.