as soon as you drive it, it dies

I have a 1998 Silverado that seems to idle for as long as you want but as soon as you drive it it dies like you turned the key off? we have had the fuel pump replaced the crankshaft position sensor, relays and fuses and checked all the wiring near the gas tanks. It does not run ruff then die it just dies turns off? and once it does it will not turn back on. we think it might be electrical? you might be able to drive five minutes or two hours its different every time. the truck has just over 200,000km and runs smooth.