How did you get to level 1000 so fast? I've been playing since end of February just before Warlords released as I hadn't long started the main Division story. I'm currently about 278 SHD and aint levelling up all that fast on Heroic with directives on like some people I've been chasing that seem to jump 20 levels very quickly.
There was a time I was catching them, 12 levels away and they seemed to jump crazy levels when I'd be playing 4 - 6 hours per night. The said people are fast approaching near 100 levels above me.
I didn't consider it fast really. I did hit Lv30 fast via the main campaign and PR from these forums running me through them. I did most of the WT1-5 on my own at which point I bought the NY DLC and then leveled to 40 in that.
Bear in mind when I began playing it was TU8 - when loot drops were really decent. After the ban patch of TU8.5 loot went downhill and never got better. So I had a ton of good quality TU8 gear in my stash that I had saved. My DPS (Infantry MG5/Glass Cannon/Vigilence) build was 95% perfected and allowed me to jump from normal to challenging difficulty without much change in my playstyle.
What changed the game for me and made me level faster was a Skill build consisting of Striker Drone/Assault Turret. I could switch on all directives on Challenging and blaze through content without too much worry and it was a great deal of fun, where with a DPS you need to really focus and be aware of your surroundings. Skill builds allow you to have freedom and enjoy things. All I do are missions, CP's (3 & 4), and the usual activities that are on a map. I don't do MP as I tend to play on and off at my age nowadays. The seasonal and league stuff give you a good chunk of XP but I am not exactly sure of the details.
https://photos.app.goo.gl/8DkdHxoAA4Kha8mT6
Heroic CP's I believe are some 530k of XP, and to level up you need 700k. Challenging is 250k or so and thats minus directives so it shouldn't be too hard. That said, if you're having fun and enjoying the solo content then just continue doing what you do. I never focused on leveling but just exploring and having a good time so nothing was really repetitous. The only sad thing is the current rewards for your time ingame - loot is an absolute disaster now.
If you do need a partner to run through a mission/bounty etc I am Kainzy on uPlay. Haven't got a mic (or a desk yet) so I tend to type with a keyboard on my lap and controller in my hand!