There isn't a 1000 frame animation limit, I don't think. Go to 'project settings' and manually(type it) change the default 'End frame = 1000' to the required number of frames. Now your timeline will reflect that.
I've never actually rendered 1000 frames, though, so I don't know if you've already tried this and found that TG stopped rendering at frame 1000, which is actually 1001, including frame '0', seems a strange amount of frames to limit to...
I'm quite sure that it isn't a limited number, however.