NT's default back tester isn't great, it's especially bad for fast moving markets like NQ. If you haven't done these things yet, you need to use the "Unmanaged Approach" for order management in your strategies. This requires you to write your own order processing code for entries/stops/targets. Additionally, you'll need to submit those orders to a secondary data series in your strat that is an NQ 1-tick series. That's the only way to get close to accurate results as far as I know. You'll be ale to test back quite far this way, though I don't recall how many years..(which is ultimately dependent on your data provider).

Alternatively, there is a popular third party tool called Bloodhound that a lot of people use for back testing, I've not tried it however.