[Roscoe]

I picked this up over at cobraforum:

Main Thing - Thanks to Wade Chamberlain's advise - Drained out the new
$13.50 / qt. GM Syncromesh Fluid, flushed it twice with 3 qts. of $1.49/qt.
Ford OEM Mercron Fluid and filled it with three final quarts of Mercron -
shifts great now. Had gone through all the Pro 5.0 shifters, new handles,
etc. So much for the "high priced spread" in the old T-5. Before this,
wouldn't shift worth a dxxx into third and sometimes 4th with the FFR stock
handle and (forum recommended) GM fluid. $169.00 Pro-5.0 shifter didn't
help very much and neither did the multiple clutch adjustments. Just plain
& simple Ford Mercron fixed it real good.