1996 Subaru Impreza car holds back when turbo comes in

Engine Performance problem
1996 Subaru Impreza 4 cyl Four Wheel Drive Manual

hi can you help please.

I have a problem with my impreza, when I put my foot down and the turbo comes in, it really holds back and jolts about, but as soon as I ease off and come out of the turbo it drives fine.

This only happens once the car has warmed up, also it has the power to pull through 1st and 2nd but when in 3rd you start to feel it holding back, with 4th and 5th being the worst, in 5th it will cause the car to start slowing unless I come out of the turbo.

I have just changed the spark and coil plugs and even the dump valve. I dont know a lot about engines but it drives and feels like its starved of fuel (or something like that) when the turbo comes in, causing it to cough and splutter under the power.

thanks mark