Sounds to me like your camera is trying to render everything off in the distance. I noticed in my old days of programming, that if I made a level on a flat ground I wouldnt have any rendering issues.
But as soon as I introduced a second layer to the ground, the fps would begin dropping.

Your model is off in the distance - what size is the texture? if its way out in the distance the camera may be trying to render everything all at once and is jamming things up.

try giving it a smaller texture just for debugging. ( iassume its big enough if your need to see texture 4000 quants away with any fine detail)