Qorvo (QRVO) had the highest return in July 1998 by a mid-cap US stock, returning 58.6%.

ASSET	MONTH	% RETURN
Qorvo (QRVO)	July 1998	58.62%
Sonic Automotive (SAH)	July 1998	28.9%
ICON (ICLR)	July 1998	25.63%
American Eagle Outfitters (AEO)	July 1998	25%
Insight Enterprises (NSIT)	July 1998	21.38%
LivaNova (LIVN)	July 1998	20%
SEI Investments (SEIC)	July 1998	19.9%
Telecom Argentina SA ADR (TEO)	July 1998	18.83%
Paramount Skydance Corporation Class B Common Stock (PSKY)	July 1998	17.09%
Granite Construction (GVA)	July 1998	16.87%
Match (MTCH)	July 1998	15.27%
IAC (IAC)	July 1998	15.27%
Lithia Motors (LAD)	July 1998	15.25%
Wintrust Financial (WTFC)	July 1998	13.92%
Valley National Bancorp (VLY)	July 1998	13.09%
FactSet Research Systems (FDS)	July 1998	12.64%
Eagle Materials (EXP)	July 1998	12.62%
Argan (AGX)	July 1998	12.5%
Embotelladora Andina (AKO.A)	July 1998	12.09%
Primo Brands (PRMB)	July 1998	10.53%
Transportadora de Gas del Sur SA ADR (TGS)	July 1998	9.97%
Embotelladora Andina (AKO.B)	July 1998	9.95%
Companhia Energetica de Minas Gerais CEMIG Pref ADR (CIG)	July 1998	9.85%
Alkermes (ALKS)	July 1998	9.72%
Louisiana-Pacific (LPX)	July 1998	9.25%

Mid-cap stocks are treated as having a market cap between $2B and $10B.