I installed a B&M Shift Improver kit in my truck's TH350. The trans was in fine shape with about 100k on the clock. It does seem to shift more firmly and 2nd lasts a little longer both of which I like. I can't say it helped my milage like they claim, but I'm happy.
The kit had the following options: Street/Strip, Towing, Street/Strip II. I chose Street/Strip since the qualities listed fit my needs most. The truck is set up for towing but the towing installation didn't do much for firming shifts or improving 2nd gear length. The S/S II was a much more involved process and the instructions said it could create very harsh shifts and increase wear and tear on the drive train. I need my truck to be reliable so I avoided this one. I also added a deeper pan with a drain plug and a trans cooler. Even before I added the cooler it seemed to run cooler after the kit was installed.
The one thing that still bugs me is that I have to put Ford style fluid in the trans per the B&M instructions. This goes against everything I've ever known about GM vs. FoMoCo transmissions and their respective fluids. It just don't seem right!
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