Mapping pstack thread number to gdb thread number

Hi folks, I have to examine a core from a multithreaded programm (with 1691 threads) on Solaris 8. With 'pstack ’ I have found the right thread I would like to examine (“lwp# 11 / thread# 11”). Now I would like to use the ‘gdb’ to examine the stack frames of that thread. So I checked with ‘info thread’ whether the thread exists and switched to it with ‘thread 11’. After typing ‘bt’ (backtrace) I saw a stack which does not correspond with the output of ‘pstack’ of thread 11. Does anyone know the mapping between the pstack thread numbers to the gdb thread numbers? Or how can I solve my problem? Markus