My 1991 Johnson fastrike model J150GLEIS has been having problems getting the last 1000rpms out of her, it use to run right up ther now I find myself waiting for the last 1000rpms to climb. I installed a jackplate in the spring and ever since then have been having trouble trying to dial it in 1st was thermostats,then redid the water pump then overheat sensors because it kept going into slo-mo when running have brought the prop to pad measurement from 6.5 on transom up to 3.25 on jackplate and no difference in rpms and someone mentioned a potential problem with power pak,a freind came by but tried to do the test according to manual and couldn't get readings for some reason.He finally got a reading off the end of the sparkplug wire and one side of motor was 1200 and the other was 900 he says he thinks this is a power pak problem and going to get worse but before I drop $250 for a new one I want to be sure any other test I can do with a simple multi meter????