how can i fix my v6 mondeo o2 heater circuit?

my 2001 mondeo 2.5 v6 has trouble codes 135,141,155 which read as o2 heater circuit bank 1 sensor 1,bank 1 sensor 2 and bank 2 sensor 1. also loss of power. changed plugs,fuel filter, leads, lambda(o2)sensors new rear cat, disconnected speed sensor and imrc.it will only rev up to 3500 rpm. has anyone ever fixed this problem as its been 2 yeare and i still cant sort it....please help