BHP (BHP) had the highest return in March 1984 by a large-cap US stock, returning 200.3%.

ASSET	MONTH	% RETURN
BHP (BHP)	March 1984	200.28%
Walt Disney (DIS)	March 1984	34.57%
Teva Pharma Industries Ltd ADR (TEVA)	March 1984	21.04%
Jacobs Solutions (J)	March 1984	20.01%
Air Products and Chemicals (APD)	March 1984	17.2%
Suncor Energy (SU)	March 1984	15.22%
Dupont De Nemours (DD)	March 1984	15.07%
Caterpillar (CAT)	March 1984	14.85%
Universal Health Services (UHS)	March 1984	14.29%
Honda Motor Co Ltd ADR (HMC)	March 1984	13.91%
Southwest Airlines (LUV)	March 1984	13.67%
British American Tobacco (BTI)	March 1984	13.17%
Sony (SONY)	March 1984	12.71%
Halliburton (HAL)	March 1984	12.46%
Gap (GAP)	March 1984	12.31%
Service Corporation International (SCI)	March 1984	11.6%
Schlumberger (SLB)	March 1984	11.04%
Travelers Companies (TRV)	March 1984	11.02%
Bristol-Myers Squibb (BMY)	March 1984	10.76%
Omnicom (OMC)	March 1984	10.76%
American Express (AXP)	March 1984	10%
Marsh & McLennan Companies (MMC)	March 1984	9.94%
Franklin Resources (BEN)	March 1984	9.52%
CSX (CSX)	March 1984	9.32%
Essential Utilities (WTRG)	March 1984	9.15%

Large-cap stocks are treated as having a market cap of $10B+.