truck died for no reson.what is my peoblum

Make sure battery has a full charge and battery connections all good. If it cranks good but won't start, have a helper crank it while you check for spark at the plugs. If spark everywhere, use a gage and check proper fuel pressure, check fuel injector pulse. Check applicable trouble codes? Those are the basic checks, in my opinion. My first two thoughts, ignition switch or your losing rpm signal? Don't replace anything w/o testing. good luck