Transmission strains (control module problem?) (archive)

I'm having an intermittant transmission problem on my 88 735i which has these symptons:
1) Occaisionally, when I'm starting from a red light (particularly uphill) the engine revs really high, strains, and seems to be working very hard for very little speed, as if I'm in 2nd or 3rd gear.
2) At highway speed, sometimes the transmission won't downshift, and the engine will run at about 3500 rpms when I'm going 65 or 70 mph. (As if its in second gear.)
Other times, in exactly the same situation, the car will work perfectly normally.
I suspect the module that controls the shifting, and have tried all of the different modes (E, S and M) to no avail.
I've been screwed a number of times at Aamco on other cars, and I'm hesitant to take it to a no name shop.

I've read that there is a transmission control module which could be to blame, and I'm wondering if others can confirm that this is the problem? Also, does anyone know how much they cost, and how hard they are to replace? (I've actually changed an automatic transmission myself, but on an old datsun.)
Any thoughts are appreciated.

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