AF1JZ,
I had exactly same problem as you described. I did all possible things like checking leaks, bov, wiring, map sensor... finally, I pulled out the twins, the turbo looks fine to me. I guess, I spent too much time diagnostic problems. Finally, I just throw in single turbo from skyline R33, simple and effective. R33 stock turbo is ballbearing type which means it should spools quicker. It started to boost at about 1600rpm and spool strong all the way, at 3500rpm I have ard 0.9bar and still going strong. I am just too "chicken" to go WOT, need to do tuning to make the car run fine.
Anyway, the only thing I didnt try was replacing the actuators. If you wanna give it another shot, try to replace the actuators. You need to replace both to make sure the turbo works together.