I have always thought this is an engineering flaw with the Tx as I have seen many rifles where there is no need to yank on the underlever.
I did find this:
Originally Posted by hollow-point
had this problem with mine. found it was the piston and spring guide touching removed half a mill from top of guide and it cocks as easy as you like now
This is good information. I found that the piston guide flange for a Prosport had to be no more than 2.8mm thick or the rifle would not cock but the antibear mechanism did engage. Tricky ...
I am not saying this is your problem but it is worth checking. Also check that guide and top hat are not contacting. This maybe could happen if a washer or washers are used on the top hat or if a too large diameter washer is used on the guide.
Cheers, Phil