If you’re on hard, dry surfaces, you can get by with a lot less tread than you think you need. Something like a Schwalbe G-One or Panaracer GravelKing SK in 2.1” would be ideal for mixed surfaces, plus it’s a higher performance option than something like the Marathons.
Get the suspension fork dialed in, as much as it’s capable of. Most people generally ride with way less preload than they need. Sure, a soft fork makes the ride “smooth” but then it also tends to bob up and down more easily.
if it has a lockout, learn to make use of it on paved sections, but try not to hit any real bumps with it engaged; that tends to put a lot of stress on dampers and seals (especially in air spring forks)
As mentioned before, just throwing a bigger chainring at it may not make you any faster, unless you’re constantly “spinning out” your top gear; ie; that the bike is going at such a speed that you can’t pedal fast enough to keep it from freewheeling. Bigger gears require higher effort per each pedal stroke; it’s much easier to train yourself to pedal 10% faster, than make yourself (a sustained) 10% stronger