Blocked govenor - ironically often caused by a change of ATF. Remove govenor and clean, change the fluid again (LR recommends 2 changes of ATF as you only change just over half of the oil when you drop the contents of the sump, the rest is in your torque convertor. I usually change the oil, drive a couple of hundred miles, change the oil again and then the filter. Only needs doing every 24K miles but still a pain. Some people never bother changing the oil for this reason!
