I just hooked up with a local Red Line distributer and am getting GREAT prices.I was curious if switching from B&M trick shift to red Line I would lose any shift firmness or shorten tranny life?Also how many quarts are needed to fill a THM 350.

Stay away from the B&M and use the Redline only, 11-12 quarts is needed to make a complete changeover. This fluid will help the transmission life.

11-12 quarts?! Are you sure? Doesn't the tranny only hold like 6qts?? When I did my last filter and fluid change I only used like 6 if I remember correctly and I had installed a tranny cooler at the same time.

Yes 11-12 quarts is normal. Stay away from the B&M fluid.Just repackaged Type F from what I've heard.Local tranny guys I know say they see a lot of varnish build-up problems with B&M and Type F fluid.Use Redline or Mobil 1 Dexron type fluid only!
You'll be much happier in the long run.
-Rich-

is it alright to use synthetic fluid in a freshly rebuilt tranny or do you need to let it break in before using it??

The guy that built my trans recommended running synthetic right from the start.
-Rich-