1996 4x4 Tahoe

We have had several problems lately. We have replaced egr valve, new spark plugs & wires, checked sensors & fuel pump, new battery & battery cables. THe battery cables would loosed up & would lose connection, & truck would go dead in the middle of road. Took it to local mechanic, kept it for 2 days & he can't find anything wrong. It is very slow to start, misses sometimes, service engine light STAYS on majority of time. The last codes that we pulled were P1406, P0175, & P0172. Anyone else with similar problems? Running out of ideas.

P1406 EGR pintle position error- you might just need to remove and clean the EGR good, if cleaning it doesn't cure the problem, replace EGR. P0172 and P0175 are rich banks 1 and 2, usually caused by faulty fuel pressure regulator and/or leaking injector lines, replace air filter first if it hasn't been changed for a while. Do a fuel pressure test, key on, engine off. The pressure should be 60-66 psi and should hold pressure after the pump quits, if the pressure drops rapidly after the pump quits check for signs of fuel in throttle body, if you can smell fuel, you should probably remove upper intake manifold and visually inspect the fuel metering body, fuel injectors and fuel pressure regulator.