My btr in my ef is playing up , It seems to slip in and out of gear when I brake , even lightly , the engine free revs when I get off the accelerator even if I have been travelling under light load . Sometimes it wont shift until 5000 rpm ,usually I have to get off the throttle at 3500 rpm then get back on it or wait for the kick in the rear as it engages I do have another out of another ef , my question is - Is there anyway of testing the spare box that's not in a car or does it have to be hooked up to the cars ecu ? and any info on what might be wrong with original box would be appreciated , I am however reading the threads that are all ready on here .

The BTRs are really sensitive to low fluid level. Just a little too low and it slips like mad. Check that first. It can sometimes be hard to get an accurate fluid level reading idling in Neutral. So, as long as you know it is not over-full, I would throw in 500mls to see if that makes a difference. If it's not fluid level, it could be a lot of things.

The BTR is computer-controlled, so it gets its shift commands from the ECU (in the 6) or a separate transmission computer (in the V8). I doubt if you could test one without being hooked up. It would have to be behind an engine to test it anyway, wouldn't it?