It is not a mod issue. I saw it the day Oblivion was released. Bethesda optimized LOD a bit, it seems to me, as they introduced new patches but I still encounter it here and there (on the road between the IC and Chorrol, for instance). It's very disconcerting to see land "snap" into place as you move forward. Oblivion's LOD, in my opinion, was implemented very poorly.