Its just a transmission that is run in many cars besides the mopars. If you cant shift it at high rpm's that suggests to me you have either a clutch or alignment issue. I would think the latter. The bellhousings need to be dialed is as well as crank end play checked. Flywheel runouts also need to be checked. Its not rocket science. To many people just toss them in and think everything will be ok. You need tools and you need to measure everything. Not everyone has the tools or knowledge to install these correctly.