Suncor Energy (SU) had the highest return in March 1988 by a large-cap US stock, returning 40.8%.

ASSET	MONTH	% RETURN
Suncor Energy (SU)	March 1988	40.85%
Universal Health Services (UHS)	March 1988	32.34%
Monster Beverage (MNST)	March 1988	32.24%
Fair Isaac (FICO)	March 1988	31.57%
Valero Energy (VLO)	March 1988	29.99%
CACI International (CACI)	March 1988	28.57%
Best Buy (BBY)	March 1988	24.97%
Johnson Controls International (JCI)	March 1988	22%
Telefonaktiebolaget LM Ericsson B ADR (ERIC)	March 1988	21.73%
Humana (HUM)	March 1988	20.48%
Stifel Financial (SF)	March 1988	18.52%
Devon Energy (DVN)	March 1988	17.66%
Teva Pharma Industries Ltd ADR (TEVA)	March 1988	17.06%
Graco (GGG)	March 1988	16.64%
Carlisle Companies (CSL)	March 1988	16.22%
ConocoPhillips (COP)	March 1988	16.1%
Williams-Sonoma (WSM)	March 1988	15.97%
Heico (HEI)	March 1988	15.91%
Leonardo DRS, Inc Common Stock (DRS)	March 1988	15.38%
BHP (BHP)	March 1988	14.57%
Honda Motor Co Ltd ADR (HMC)	March 1988	14.37%
Aflac (AFL)	March 1988	14.03%
Coeur Mining (CDE)	March 1988	13.85%
Kinross Gold (KGC)	March 1988	13.16%
Magna International (MGA)	March 1988	13.06%

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