trans problem with 300E

[300EVIL]

for some reason my trans isint catching correctly when slipping into third gear.
it mostly occurs when im accelerating harder than usual. sometimes i catch it when its about to then i let off the gas and it kicks into third. but when i dont the engine revs all the way up! outch! the problem seems to get worse every week. my MB tech says i should try adjusting the shift points by turning the adjustment screw behind the air cleaner housing, is this a good idea? yes, i did check the ATF level.
your responce will be greately appreciated
thanks,
adam

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