Could be mental. For example, when I'm 2000 blitz and I play a 1800 opponent, I generally will beat them. However, if I get in a slump and drop down to 1800, I find it can be very difficult to beat an 1800. I think it has to do with confidence and it works both ways - when I'm 2000 I feel confident I should beat the 1800 and he might not feel very confident - but if I am 1800 I have less confidence and he has more.
You might get close to 2000 and start to doubt yourself. Just keep playing your best chess and concentrate, and you will get there soon.
I've reached 2000+ on soooo many other chess sites, but yet i cant seem to crack 2000 on here. Heck, my highest is 2126 on one of those sites, but no, cant get higher than 1996 on here. I mean i realize chess.com has the most comp, but 130 rating difference is very odd, dont you think? Is it just a mental thing this point instead of actual skill?