If happening when under load and going uphill it will be a fuel fault .,do the basics as in fuel filters .blow the lines back and if it still happens you may be looking at injectors …A lot of fuel came in from russia to the south east of the country ,and the boats where not quiet as clean as they should have been …All manufacturers have suffered issues due to the tolerances of the fuel components the dirt that gets throw sandblast them then you get excess leak off …The jocks fuel came in via grangemouth and on percentage wise there where a lot less issues and it didn;t come from russia