Bank of America's Michael Hartnett expects a stagflation scare this autumn, which is bad news for stocks, truckers, and anyone already squeezed by high costs.

• Diesel, not oil, is the real pressure point — it moves shipping, trucking, farming, construction, and mining.
• Diesel is more expensive now than it was in 2008, even though oil was pricier back then, partly because of higher taxes since.
• Truckers say the numbers no longer work: a full tank can eat the entire day's profit on a job.
• The 30-year government bond yield is the highest since 2007 and oil is back near $100, yet nobody seems worried — and markets usually only stop panicking once policymakers start.
• Transport stocks are sitting right on their long-term trend line; if they break down, it confirms that summer was as good as it gets.

Outlook: If diesel stays high and transport stocks crack, expect investors to pull back on risk and a rough stretch of inflation plus slow growth heading into the fall.