I have a 99 k1500 Suburban 4 wheel drive with 135,000 miles. I have a very hard start problem, i have replaced the fuel filter, fuel pressure regulator, plugs, wires and my buddy did a fuel injector balance test and they were all good. I had codes of p0171 and p0174 which is misfire and it said to do the fuel injector balance test which we did and was ok, the fuel pump puts out 60 psi at start up and 50 psi while running. When i get it started it runs great with no problems. Any ideas on what to do next?