Updated from 11:33 a.m. EDT

There wasn't much pep in

Pep Boys

(PBY) - Get Report

on Thursday.

Shares in the Philadelphia-based auto-parts retailer plunged 28.5%, perching them atop the

NYSE

percentage-losers board, after the company posted weak second-quarter numbers and shuffled its executive suite.

Blaming weak sales on its service side, Pep Boys posted a second-quarter operating profit of 29 cents a share on sales of $593.4 million. The earnings came in 8 cents shy of the Wall Street consensus. A year ago, the company earned 30 cents a share on sales of $556 million. The company also named Harry Yanowitz chief financial officer, and said President George Babich will take responsibility for rebuilding the struggling service business. Shares of Pep Boys dropped $5.42 to $13.59.

Washington Group International

(WGII)

rose 8.9% after posting better-than-expected-second-quarter results and boosting its full-year outlook. The engineering company posted a second-quarter profit of 49 cents a share, exceeding the Thomson First Call estimate by 3 cents, on sales of $684.5 million. Looking ahead, Washington expects to earn around $1.89 a share for the year on sales of around $2.9 billion. That's up from previous guidance of $1.60 a share on sales of $2.55 billion. Analysts had expected the company to earn $1.94 a share on sales of $2.65 billion. Shares rose $2.88 to $35.09.

Shares of

Tiffany

(TIF) - Get Report

fell 14.8% after the company posted soft second-quarter numbers and warned of a third-quarter shortfall, citing weak results in Japan. The high-end retailer posted a second-quarter profit of 25 cents a share on sales of $476.6 million. Analysts expected it to earn 29 cents a share on sales of $496.1 million.

Looking ahead, Tiffany expects third-quarter earnings to be on par with year-ago results, at 19 cents a share. Analysts had expected it to earn 23 cents a share. For the full year, Tiffany forecast earnings of $1.55 to $1.60 a share, below the consensus estimate of $1.63 a share. Shares traded down $4.70 to $27.10.

Matrix Service

(MTRX) - Get Report

fell 26.6% after posting a weak quarter and trimming its 2005 outlook. Excluding items, the industrial services company posted a break-even fourth quarter on sales of $133.1 million. Analysts had expected it to earn 3 cents a share on sales of $124.3 million. Looking ahead, the company forecast 2005 earnings of 60 cents to 70 cents a share on sales of $475 million to $525 million. Analysts were expecting it to earn 70 cents a share on sales of $512.7 million. Shares of Matrix Service traded down $1.81 to $5.

Shares of

Plato Learning

(TUTR)

fell 23.4% after the company warned that its third quarter would fall short of expectations. The education solutions company now expects sales of $40 million to $41 million. As a result, earnings also will be less than anticipated, though the company didn't quantify the shortfall. Analysts had expected Plato to post third-quarter earnings of 35 cents a share on sales of $43.4 million. For the full year, Plato expects sales of $143 million to $147 million, well short of the $150.4 million analysts were expecting. Shares of Plato Learning traded down $2.05 to $6.71.

NYSE volume leaders included

Hewlett-Packard

(HPQ) - Get Report

, down $2.57 to $16.95;

Lucent

(LU)

, down 16 cents to $2.70;

Corning

(GLW) - Get Report

, down 89 cents to $9.77;

EMC

(EMC)

, down 66 cents to $9.48; and

Nortel Networks

(NT)

, down 12 cents to $3.23.

Nasdaq

volume leaders included

Cisco

(CSCO) - Get Report

, down 50 cents to $17.79;

Intel

(INTC) - Get Report

, down 92 cents to $21.24;

Oracle

(ORCL) - Get Report

, down 29 cents to $9.90;

Microsoft

(MSFT) - Get Report

, down 53 cents to $26.88; and

Sonus Networks

(SONSE)

, down 38 cents to $3.70.