Les in his dotage is probably refering to the TR3550 which is sometimes called the 5speed toploader.
A significantly tougher transmission than the T5. The standard units are rated at 350ft/lb of torque where your T5 is rated to about 230ft/lb.
there are some beefier versions of the 3550 as well with the TKO II is rated to 475ft/lb.
You could also look at the T56 6 speed which is rated at 450ft/lb with beefier versions rated up around 650ft/lb.
Check out the Tremec web page for details on the different transmissions they make :
Tremec T5
Cheers