Our frame#6B GT with breech loaded fuel nozzles tripping suddenly on high spread while in liquid service.Before the spread started raising unit was running normal with very minimal spread (spread#1 was around 15) at the time of spread no.6 nozzle pressure in selector valve was 7kg more than all other nozzles.No deposits or blockage is seen on the no.6 tubing with BI also No.6 fuel tubing replaced with new one from flowdivider outlet to fuel nozzle inlet but no improvement.