Vw passat 1999 1.8 t has loss of power. Won't go over 40 ...

Vw passat 1999 1.8 t has loss of power. Won't go over 40 mpg. Or over 3000 rpm unless first started. I have replaced mass air flow sensor, the turbo, exhaust and intake manifold gaskets, the fuel filter, replaced crankshaft breath...

Vw passat 1999 1.8 t has loss of power. Won't go over 40 mpg. Or over 3000 rpm unless first started. I have replaced mass air flow sensor, the turbo, exhaust and intake manifold gaskets, the fuel filter, replaced crankshaft breather assembly, changed spark plugs, ran lucas fuel cleaner through it, cleaned top end of motor, tested fuel pressure--55 psi at idle, 60 psi at acceleration, only ran 91 octane fuel and octane boost helps but doesn't eliminate problem. Slow to accelerate, no power for even slightly steep climbs. Was misfiring cylinder 1 but after spark plugs replacement no longer misfiring. Have not replaced air/fuel regulator sensor or fuel sock in tank. Mechanic's Assistant: Is the power loss consistent, or does it fluctuate? Consistent with not going over 3000 rpm or 40 mpg. Sometimes it will surge and at first start has more power then after running even for a few minutes Mechanic's Assistant: Are you fixing your Passat yourself? What have you tried so far? Yes and listed in first message