Boost problem - 98' STi
 

Ive just come into a bit of a boost issue with the car yesterday. Car should acheive 1.2 bar but only boosts to 0.6/0.7 bar. Im seeing this on my Power FC.

If I keep my foot down once it gets to around 4-5k, most prominently in 4th and 5th gear. Its jolts forward like it hits a wall. Ive read into boost cut but its not overboosting from what I can see on the Power FC. Ive had a look already for any split pipes but havent come across anything.
Ive also ordered up new plugs but it doesnt feel like it would be caused by plugs as it doesnt actually feel like a missfire as such.

Only other things I can think of are faulty boost control solenoid or a dodgey actuator ? Although ive checked the actuator rod and its not rusty and still has its tensioned sprung movement?

Any ideas? Car is a 1998 STi Type R
Decat turbo back and air filter basically.

Boost solenoid was the issue for me, bought a new one from Subaru and it solved it