FRUEHAUF CORP. (Detroit) - T. Neal Combs has replaced Robert D. Rowan as chairman. Mr. Rowan officially stepped down last week as Fruehauf's chief executive.

Mr. Combs was Fruehauf's president and chief administrative and financial officer since 1986.Mr. Combs then named John J. Garber vice president and controller. Mr. Garber was vice president and controller for Kelsey-Hayes Co., a Fruehauf subsidiary.

John P. Kenny was appointed to the new position of vice president, chief information officer. He was vice president, information systems for Kelsey- Hayes.

IVECO TRUCKS OF NORTH AMERICA (Blue Bell, Pa.) - James Underwood was promoted to senior vice president of sales, with responsibility for dealer sales and national accounts. He was senior vice president of dealer sales.

Iveco sells light and medium-duty diesel-powered trucks.

P.A.M. TRANSPORTATION SERVICES INC. (Tontitown, Ark.) - John Karlberg was elected president. He succeeds Paul A. Maestri, who remains chairman and chief executive officer.

Mr. Karlberg, a 24-year transportation industry veteran, was vice president of Sun Carriers Inc. from October 1987 through April 1988 and president of Jones Truck Lines Inc., a Sun subsidiary, from January 1980, to October 1987.

P.A.M. Transportation is an irregular route common and contract truckload carrier.