long distance PCR and Tth?

[Tay Hou Ngee Agnes]

Hi
Does anyone have any experience with the different Tth DNA polymerases 
for long-distance PCR using genomci DNA as template? I 
was trying out the Human promoterfinder kit from clontech but they had no 
enzyme in stock so I substituted Tth from promega and have blanks.
Would appreciate any advice on longdistance PCR esp with genomic dna as 
template.
Thanks a lot
Agnes