HELP!!

I have a 94 model 9000 2.0 ecopower. I've just had it for a few weeks and
the previous owner had replaced sections of the exhausts. Anyway, the
exhaust has been blowing slightly in a couple of places - (1) where the
front pipe joins the turbo and (2) between the cat and the mid section. So
armed with some gun gum I patched things up. (Wish that would work with the
wife!) It's now quieter, smoother, more responsive and more
economical....BUT, and I don't know if this is connected to what I did
with the patching up, since I patched it up I can't use full throttle
anymore. Half to two thirds on the throttle is ok but anything more and
from about 3000 rpm the car just kangaroos down the road. It's as if the
engine keeps cutting off the fuel supply. However, it's fine when I rev it
in neutral and also on part throttle its happy to go all the way round the
rev range without a hiccup. So anybody with any ideas out there?

Oh, please keep it simple. I am as about mechanically minded as, well, a
kangaroo.