there is no interval for replacing the head gasket. that should only be done if there's enough damage/wear to warrant it.

those compression numbers are fine. the 170s may indicate minimal head gasket wear between those cylinders, but definitely nothing to worry about.

driver, if you're referring to the valve cover gasket, that has nothing to do with your issue of running lean. yes, you should replace it every time the valve cover is removed (i.e. when you adjust the valves) but all that gasket does is keep the valve cover sealed.

just to make sure you're clear on this, valve cover gasket does not equal head gasket. your issue of running lean is being caused by something else, i'm almost sure of it. when's the last time you replaced things like the fuel filter, spark plugs, etc.?