Strange problem with autovacuum

Hello list.

I have a strange problem with one of our servers (PostgreSQl 9.2.8).
Every monday the autovacuum workers seems to stop working (the workers
decrease in number) this causes that 5 tables that are constantly
updated and deleted to be really slow.

I have this settings on postgresql.conf:

maintenance_work_mem = 7936MB
autovacuum = on
#log_autovacuum_min_duration = -1
autovacuum_max_workers = 12
#autovacuum_naptime = 1min
#autovacuum_vacuum_threshold = 50
#autovacuum_analyze_threshold = 50
#autovacuum_vacuum_scale_factor = 0.2
#autovacuum_analyze_scale_factor = 0.1
#autovacuum_freeze_max_age = 200000000
#autovacuum_vacuum_cost_delay = 20ms
#autovacuum_vacuum_cost_limit = -1

Per table I have this settings:

datosr

  autovacuum_enabled=true,
  autovacuum_vacuum_threshold=50,
  autovacuum_vacuum_scale_factor=0.1,
  autovacuum_vacuum_cost_limit=1000

datose

  autovacuum_enabled=true,
  autovacuum_vacuum_threshold=50,
  autovacuum_vacuum_scale_factor=0.1,
  autovacuum_vacuum_cost_limit=1000

idig_h

  autovacuum_enabled=true,
  autovacuum_vacuum_threshold=1000,
  autovacuum_vacuum_cost_limit=2000

iodig

 autovacuum_enabled=true,
  autovacuum_vacuum_threshold=1000,
  autovacuum_vacuum_cost_limit=2000

ia
  autovacuum_vacuum_threshold=50,
  autovacuum_vacuum_scale_factor=.1,
  autovacuum_vacuum_cost_limit=1000

I bases those settings by reading this blog entry:
https://blog.2ndquadrant.com/autovacuum-tuning-basics/

It seems that I am doing something wrong, could you guys please point me
in the right direction?

Thank you very much