Sipsipding

I no it’s old thread but wondering if you figured it out I’ve got same problem

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 .

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