The Short Version
This claim is false. Snopes traced the "diesel to gasoline" suggestion to a satirical post on Fazzler.com, a known satire website. No credible news source — including Al Jazeera, Transport Topics, KIRO 7, and CBS Evening News, all of which covered Trump's actual fuel-cost responses in March 2026 — recorded him making this suggestion. While Trump did address rising fuel costs through measures like a Jones Act waiver, the specific claim about advising truckers to switch fuels is fictional satire, not a real statement.