I'd switch off GI completely and render it with a multi directional sunlight setup.
If you look in your program files folder(assuming you use PC version) go to this location; 'Planetside Software' >> 'Windows' >> 'Generic'. You'll find an alternative default scene there called, I think, 'default_pre_GI.xml'. This will give you an empty scene the same as the default scene but, with a multiple sun lighting setup instead of a GI based one.
Open this .xml like you would any other TG project, copy the 3 sunlight nodes(or save as a clipfile to use again) to your animation scene then, set GI detail and GI quality both to '0'.
Try rendering a few frames that you know were problematic and check the results, I think you'll find a dramatic improvement in the lighting flicker.
As for the terrain flickering, that isn't as bad as the lighting issue but, do you have 'detail blending' set to '1' or, is it still set to the default of '0'? If it's set to 0, set it to 1. This will increase render time, though.
EDIT: Hee-hee! ^^ Hi, Martin.