Help with video problems

This used to happen in Halo 3, but I never cared because the game wasn’t big enough to be affected. Basically, objects that are very far away do not appear or are shown in low-res textures that would be better in Doom. A rock from far away looks like a smooth gray sphere. Worse, enemies that are shooting at me from half-way across Hemorrhage do not appear unless I use my scope. Even the Warthog is invisible until it’s within lethal distance. The enemy can see and shoot me before I can.
I have an LG HD LED TV. I have my 360 set to 1080i (or p, I can’t remember). My TV is set to game mode. The problem only happens on very large maps, and is very frustrating. It basically ruins BTB and Invasion. Objects that are affected are either invisible, completely un-textured or covered with a repeating pattern of triangles.

I first noticed this with Halo 3, but it wasn’t as much of a problem at the time. Now, it SUCKS.

Please, help me.