I have a 1990 Suburban (156k miles, 350, automatic, 4X4) that hesitates and stalls when under a load. When it is in park or in neutral, it runs very well and is responsive to the gas pedal. However, whenever there is an engine load (like when holding the brakes or accellerating rapidly) it looses power and acts like it is choking out. I have an intermittent check engine light which reads a code 44 (lean exhaust). We changed the oxygen sensor, plugs, wires, distributor cap, fuel filter, and also put a new gasket between the carb and air filter ring. Both the throttle position sensor and MAP sensor check out OK. What should I check next? Any help would be greatly appreciated, thanks!