Waste Management (WM) had the highest return in March 1991 by a US stock in the S&P 500 (GSPC), returning 51.8%.

ASSET	MONTH	% RETURN
Waste Management (WM)	March 1991	51.79%
Amgen (AMGN)	March 1991	37.98%
General Dynamics (GD)	March 1991	32.68%
Advanced Micro Devices (AMD)	March 1991	31.25%
UnitedHealth (UNH)	March 1991	30.83%
Trimble (TRMB)	March 1991	28.72%
Johnson Controls International (JCI)	March 1991	28.57%
Bio-Techne (TECH)	March 1991	28.12%
Raymond James Financial (RJF)	March 1991	27.73%
Kroger (KR)	March 1991	24.84%
Constellation Brands Inc Class A (STZ)	March 1991	24.32%
Western Digital (WDC)	March 1991	22.86%
Fastenal (FAST)	March 1991	22.77%
Williams-Sonoma (WSM)	March 1991	21.92%
PNC Financial Services (PNC)	March 1991	21.69%
Lam Research (LRCX)	March 1991	21.26%
Viatris (VTRS)	March 1991	21.03%
MGM Resorts International (MGM)	March 1991	20.88%
Valero Energy (VLO)	March 1991	20.64%
Electronic Arts (EA)	March 1991	19.84%
McCormick (MKC)	March 1991	19.52%
Hologic (HOLX)	March 1991	19.35%
Bank of America (BAC)	March 1991	19.33%
Apple (AAPL)	March 1991	19.3%
Laboratory Corporation of America (LH)	March 1991	18.18%