'89 Ford Ranger Transmission & Over-rev

[damnthemachines]

Hey, I bought an '89 Ranger (2.9 V6 A4LD transmission) a while back and the transmission was shot. So, the guy tells me that there's another transmission on an '85 (2.8 V6 A4LD transmission) Ranger that we can have. We took it, dropped it in, and still had problems with the Ranger over-revving like crazy. (3000 RPM @ 55mph, 4000 RPM @ 70mph) Both transmissions were 3 speeds with an overdrive, automatic transmissions. The engine itself doesn't sound like it's under a lot of stress, and I'm starting to think maybe the gauges are telling me wrong. The tachometer took a while to go down to 0 when I turned the engine off and the gear indicator is loose and doesn't always show me what gear I'm actually in. My girlfriend's stepfather, mechanic, tells me that the transmission I pulled definitely worked fine. I didn't take the flywheel, but I did get the torque converter. The only difference in the transmissions was a plug on the side. The '85 had a two-prong, and the '89 had a three-prong. We wired it in so it would work. If there are any problems with the transmission conversion, it's there, but I just don't know what to think due to the sound of the engine and the crappy gauges. Any ideas how to test this for sure? Or change those plugs? I believe the plug is for the overdrive and torque lockup converter. (Not sure.) Any help would be greatly appreciated.