converter slipping

yeah....thought the 2.75's would make brake in miles easier on the wallet. did not expect the effect it had on driveability. not driven a car with such a converter before now.
are the soft shifts at lower rpm a result of the slip as I've been told? at upper rpm they were firmer.
have solid engine mounts and oem style trans mount. did notice a shudder at medium to heavy acceleration. could this bi the trans mount. trans is new build.