I have a 1995 Chevy Silverado 4x4. I have had at to 3 different mechanics. When on the highway and I try to excelerate to pass the truck falls on it's face (cuts out but don't die) then when it get up to speed it regains power. This also happens at stop signs, idols real rough, but not all the time and it is usually warmed up before it does it. The last 2 mechanics changed the egr valve and thermostat and ran machines on it. Please help.