Unoptimized Engine or secret Bottleneck?

Hey Guys! I have a question regarding bottlenecks and game engines.

 So recently I have been extensively performance testing a new flight simulator software (P3Dv2).

 It's engine by core is a pretty old one (based on FSX's ESP engine from 2006) but the graphical rendering part of it said to be redone completely utilizing all the bells and whistles of DX11.

 I first had a weird issue about multi core utilization, but that was a windows issue and has been sorted out so now it nicely utilizes 3 cores out of 4 as it should be for the best performance.

 The hardware monitor chart looks like this:


Bottom: Core 0

Pink Straight line: RAM

Middle thre lines are working cores

On the top is the GPU load

 That looks perfectly good for a game, no bottlenecking as far as I see BUT during this benchmarking session I had 5fps! What we cannot see here although is the VRAM usage, so I was logging it with GPU-z separately. Far away from being a bottleneck as well 2.1Gb max from the 3 Gigs.

 So what can be the problem? Very bad optimization? Bottleneck I didn't take into consideration?

 I'm open to any bright ideas because I'm stuck. (BTW just in comparison the original dx9 version of the same engine from FSX runs around 100fps in comparison)

 System specs:MSI mpower Z87, 4670k @ 4.4Ghz, HD7950 @ 1160/1550Mhz, 8Gb Kingston HyperX @2133Mhz, one screen setup 1080p res.