Re: 2000 Taurus transmission issue
"at exactly 1500 RPM (whether in overdrive or drive) the transmission starts slipping, or going in and out of gear, or trying to decide which gear to be in."
One possibility is that the transmission is "hunting", i.e. the sensors that control electronic shifting are reading that the load is right on the border between continuing in the present gear or downshifting, so the computer initiates a downshift, then decides to cancel it and remain in the present gear. I've encountered this in other vehicles, so it's not just a Ford problem. It seems to occur when driving at low rpms in vehicles in which the drivetrain programming is leaning more towards economy rather than performance. My only complaint about my 2000 SES with the Duratec engine has been that the shifts are "mushy" under partial throttle, almost feels like the transmission is slipping. Ford techs say that is by design; programming for sharp, crisp shifts would mean rapid downshifts under partial throttle, resulting in lower gas mileage. Several of the performance EPROM chip suppliers claim improved shifting as part of their performance enhancement.