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%
Jacobs Solutions (J)	March 1984	21.83%
Teva Pharma Industries Ltd ADR (TEVA)	March 1984	21.04%
Caseys General Stores (CASY)	March 1984	17.38%
Air Products and Chemicals (APD)	March 1984	17.27%
Smith AO (AOS)	March 1984	16.51%
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	13.69%
British American Tobacco (BTI)	March 1984	13.04%
Sony (SONY)	March 1984	12.71%
Gap (GAP)	March 1984	12.27%
Service Corporation International (SCI)	March 1984	11.6%
Schlumberger (SLB)	March 1984	11.04%
Travelers Companies (TRV)	March 1984	11.02%
Omnicom (OMC)	March 1984	10.76%
Bristol-Myers Squibb (BMY)	March 1984	10.75%
Franklin Resources (BEN)	March 1984	9.7%
CSX (CSX)	March 1984	9.32%
Essential Utilities (WTRG)	March 1984	9.15%
Toyota Motor Corporation ADR (TM)	March 1984	9.09%

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