Does it crank OK?
If it cranks OK check engine compression. If the problem is that it cranks too slow to get it started then I would suggest you check your electric starting system. Check the state of charge of your batteries, check the heavy gauge cables, check that connections are tight and clean. If the problem persists have the starter itself checked. We have the same engine and in really cold mornings I may need to move our battery switch to "All" just to make it easier to crank. Make sure your engine is operating to specs before considering any gadgets.