Bear Stearns ( BSC)stumbled after the Wall Street investment firm was downgraded by a Punk Ziegel analyst to market perform from buy. Bear Stearns was one of several big name brokerages downgraded Tuesday by Punk Ziegel. Shares were trading down $3.52, or 2.63%, to $130.38. Credit Acceptance ( CACC) gained after the Southfield, Mich.-based auto lender said it plans to buy back up to 3.5 million shares in a modified Dutch auction. Credit Acceptance expects to pay between $28 and $31.50 a share in the offering, which will expire Sept. 26. The company said Donald Foss, chairman and majority shareholder, indicated his non-binding intention to tender 20 million shares. Credit Acceptance has 33.4 million shares outstanding. Shares were trading up 30 cents, or 1.07%, to $28.24. First Horizon ( FHN) slipped after the Memphis, Tenn.-based financial services company warned that its third-quarter results would be hurt by a weakening mortgage market. The lender now expects third-quarter earnings to come in about $35 million lower than the second quarter. The company also will record a $21 million charge related to the settlement of a class-action lawsuit. Shares were trading down $1.97, or 4.92%, to $38.08. CNA Surety ( SUR) stumbled after the Chicago-based insurance company was downgraded by Deutsche Securities to hold from buy. Shares fell $1.33, or 6.12%, to $20.39. Ocwen Financial ( OCN) sank after the West Palm Beach, Fla.-based savings and loan was downgraded by Piper Jaffray to market perform from outperform. Shares fell $1.81, or 11.21%, to $14.34.