Low FPS after upgrades - Help Needed

[Slimer]

OK I am turning to these forums in hopes someone can help me. I recently bought a VFC Socom Daniel Defense M4. I am having the following items installed in it by a professional tech, but have run into a problem, its only shooting 320 FPS. When it should be around 380-390. I am hoping someone here can help us figure it out.
All factory internals have been replaced, except for the stock mechbox. Upgrades include

Lonex 70degree bucking
R Hop
M Nub
Lonex Metal 1 piece hop up
Angel Custom TBB Barrel
SHS high Speed Gear Set
Lonex Piston & Piston head
Lonex Cylinder & cylinder head
Mosfet installed
Lonex Titan a2 motor
AOE Correction
TX Bushings
Sorbo pads installed
M120 Spring (slightly used) last tested it output 396fps
Re-shimmed and greased
Any ideas what could be causing the low FPS issue?

[Deleteplz]

Check the following for compression leaks, hop-up bucking, airseal nozzle, piston head and cylinder head. Most of the airseal issues I've seen are due to bad o-rings on the piston head or cylinder head.

[Reeko]

Its the R-hop. they will significantly lower your fps. I put an ER-hop in my gun and it dropped to 315fps (from 380). I still get great range even at 300fps though.

Thats with a polarstar with a blue nozzle. So the mechanism is pretty standardized. I was shooting at 90psi. with a 6.03mm barrel.

and the sorbo probably contributed as well , they usually cut down on compression a bit.

i could be wrong though.So Try it with a regular hopup and see what happens.