No, you should not have MacTCP running on PCI-based Power Macintosh computers. Prolonged use of MacTCP can damage system software to the extent that Open Transport networking will not work properly. If Open Transport no longer functions properly, you need to perform a clean installation of the system software as described in the Power Macintosh User's Guide that came with the computer. The information below is from the PCI-based Power Macintosh Read Me files, and it recommends removing MacTCP.
Important Information About Open Transport Networking
MacTCP
After you install new networking software on your hard disk, if you have problems with TCP/IP applications, look in the Control Panels folder for a MacTCP file. If one is there, remove it from the Control Panels folder and restart your computer. Each time you install new networking software, you may want to verify whether or not the software's installer also installed MacTCP, and follow this procedure.
Article Change History:
08 May 1996 - Included additional information on clean system install.