Supra slow to pick up power

[downunder]

Hi

I am wondering if anyone might have any ideas on this problem that has developed with my 87 MA 70 Twin Turbo. One owner.

Had local mechanic look at it who has done good work on this car before and he cannot find the problem.

He has checked things like fuel and air filters, cylinder compressions, intercooler and the pressurizations, changed plugs, checked timing etc.

Problem is – it lacks power up to around 3000rpm.
It seems to nearly reach around 3000rpm when the first turbo I think should be cutting in but then the revs drop to around 2500. When the turbo does cut in at around 3-3500 there is plenty of power. To me its like the automatic transmission is not going the gears smoothly like it did before.

Any help would be most appreciated