03 xr6T ute with 06 typhoon motor 5 speed manual

[Sipsipding]

Hi guys new here first post hopefully you guys can shed some light 

so problem comes and goes with no pattern . 

When driving if ya lean on it will not boost over about 3 or 4 psi and starts breaking down liken plugs/coils are giving up spluttering and surging and as quick as it came you can lean on it and it’s spinning 15 psi and cracking 

ive changed fuel pressure Reg 
I thought waste gate was sticking but no 

it’s got new plugs genuine coils new recently new fuel pump 

doing my head in 

[k31th]

 

so it's definitely tuned... has it always done it since it's been tuned?

[Sipsipding]

It got tuned on dyno And then started doing it couple hours later 

 

I went for run last week end 430 ks and it ran great for bout 300 ks then ran the worst it ever has rest of the way .