I have a 2000 Chevy Suburban K1500, 4WD, 5.3L. While driving I noticed the service engine soon light was on. Truck was running fine so I figured I would check when I got home. Was driving on some country roads, so I didn't really get over 40 mph. When I finally got out on the highway, I noticed that at 70 mph. the engine rpms were higher than normal. Well, I figured out that it wasn't shifting into overdrive. When I did shift down to 3 you could feel it downshift. When I shifted down to 2 you could feel it downshift. When shifted down to 1 it didn't downshift. It acts like it's one gear off from what the shift indicator says it is. The weird thing is it will shift into reverse, nuetral, and park properly. If you come to a stop and manually put it into Drive 1, It acts like it is in Drive 2. i know it has that special driving thing where if you manually put it in Drive 2 when you take off it takes off in Drive 2. I checked fluid level (OK), not burnt smell. Drove home from vacation home (130 miles) yesterday and drove fine (excluding the higher rpm and higher fuel consumption understandably) but won't shift into OD. Engine light/no OD related or coincidence. Both symptoms happened at same time. Any ideas!