I'm currently level 34 on my second character (First character is 1332 but glitched and won't receive a call from Simon about Apartments) and I'm finding it a pain in the *** when it comes to leveling up.
People seem too focused on Money glitches than RP Glitches these days.
My suggestion is to play missions until you are able to do Heists. Do races or actual missions. Another option is go to the Grand Theft Auto V Matches forum on here and find people to boost with. It's not as common but you might find other low levels to help rank you up quick.
Hope you find a way that works for you and that you rank up fast . Good luck.