It's what Bob and others said. Dish changed how they downloaded guides several years ago and that made the pict in guide feature useless on the 4900. It also made searching more than an hour in advance a painful experience. The situation will never improve, and if it bothers you the only solution is a new receiver. I would suggest a PVR and never look back.
We have a 508 PVR and a 4900. The 4900 is on a kids TV, because they never care beyond what is on right now. We have also disabled the picture in guide feature because it is pretty much useless these days. You can turn it off in the menus.