RoTarY!!!a_t_w

i have a 87 turbo II and i am having a problem boosting....so here is the best way i can discribe it.....i can go all the way through the rpms in first....but once i shift into second and hit around 4k rpms it studders and it wont go any higher and its around 3500rpms in 3rd and 4th around where it starts hitting boost.....hard.....i dont know if it has something to do with the wastegate not working right or the turbo.......but if someone could help me figure this out it would be greatly appreciated thanks