recently purchased a 2001 B-3000. 6 cylinder, 4 wheel drive. twice recently, once the truck was started, check engine light came on and oil gauge showed no reading whatsoever. as soon as i turned the engine off then restarted, everything worked fine. while on the highway, my OD light suddenly began blinking. when i stopped for gas and restarted the engine, the blinking stopped. twice today, when i turned the engine off, and tried to restart, the engine would crank, but it took a long time to start. when it started, the 4 wd, low light came on. the 2nd time, same difficulty starting after turning engine off, and when it started, 4 wd high light came on. anyone have ideas as to what the problem might be?