tsearch2 document and word limit

Hi

I have been toying with the implementation of tsearch2 to index some large
text documents. I have run into problems where I am up against limits:

no more than 255 occurrences of a particular word are indexed.
word positions greater than 16384 are added as position 16384 and end up as
one occurrence.

These are problematic because I need to rank based on number of word
occurrences, and these limits are preventing this.

Does anybody have any suggestions as to how this could be worked around, is
the limit due to gist? would openfts help (im guessing not)?

Failing that does anybody have experience of combining another text indexing
package with postgresql?

Dave