Why does truck keep skipping or cutting back?

Hello, what kind of test equipment will guess at component failures? The only proper way to test is to retrieve trouble codes which require troubleshooting. Part replacement -- when needed -- comes due to test results found. As a result, I'm not entirely sure you needed an oxygen sensor or a mass air flow sensor. What trouble codes are you getting now? Your symptom is indicative of an engine misfire, or a timing issue, or a compression issue, or an air intake issue. Too hard to tell without hands on testing using proper equipment that can monitor data of components.