I have a new TCI 3500 stall in a T-350 and after I installed a b&m shift kit the dang
thing rattles like there are loose parts in it. It is loud and I had it up on
a lift to check to be sure thats where the noise is coming from. Only does
it in gear. Gets quiet in park. Whats up??? Car operates and trans shifts
well.

Check the converter bolts to make sure they are tight.

very tight

I assume that you had the tranny out of the vehicle since you indicate that the 3500 is new? If so, it may be the converter was not installed correctly...there should have been two "clicks" when sliding it back over the input shaft, otherwise, it will run the vehcile but not "fully" engage...

Also, if not properly installed, you can damage your "pump" drive in the transmission...

Kieth, Steve, ignorant me did not check the convertor bolts with a wrench,
just look at them. THey are fine thread that thread into the convertor from
the oil pan side. Slightly loose when I put a wrench on them. The engine
just went in two hours back and they were tight, thats why I did not look.
This time loctite on the threads. Thanks for the help

I'm glad you found the problem. :beers: