1992 Chevrolet c1500 5.7 l code44 code 34 which is lean fuelair changed fuel filter o2 sensor. map tps egr ok local parts store not much carbon in egr or manifold What else could it be?

It sounds like you've checked a lot of the usual subjects but there are a couple other possibilities that you might consider. Check for low fuel pressure. The pump or pressure regulator might be worn resulting in an inability to deliver enough fuel. Another possibility would be a vacuum leak. Check the manifold gasket, the gasket between the throttle body and the intake manifold and any of the vacuum lines, such as the brake vacuum boost line. Leaks there will also result in a lean running condition. If you suspect a leak, try a little starting fluid sprayed right on the part that you suspect is leaking while the engine is running. If the engine suddenly runs different, that's probably the leak.