I know this is an old thread but it's on the first page of google search (fm145,strength,tq ratings) so I thought I'd add some info about the 5th gear issue. The bearing against the 5th sincro expands and shifts during towing and high trans heat operation. It than cools and gets stuck against the sincro causing intense friction heat and results in the bearing and sincro welding to 5th gear. Now this is just a summary of the article on the issue which I suggest you read
http://autotransmissionblog.com/ford-ranger-5-speed-fm145-fm146-5th-gear-problem/
There are now fixes for this issue available on the market making the fm145 a good daily driver trans, And with today's cryogenic treating process you can get your trans internals cryo treated adding an additional 20-30% strength over stock. So swapping isnt the only option.