I have a 1995 Chevy Blazer with a 4.3 litre vortec engine. The engine only has 20k. I have replaced the fuel pump, sending unit, and the fuel filter. When the vehicle is driven up a hill it spits and sputters. After about a week of normal driving conditions or if driven a long distance in a day. The fuel will no longer come out from the injector tips into the manifold. After the vehicle sits for 3 or 4 days then it will start normally. I have also replaced the computer twice to ensure that this was not the problem.