1991 shadow 2.5 turbo over boost loss of power on highway

[bill]

i have a 1991 shadow 2.5 turbo and am haveing over boost shut down plus loss off acceleration going down the highway i would really like to know the common problems for this and a basic veiw on how this works i know its got to be a westegate problem but were to start vacuum, selaniod or is there more, tps or maybe a wiring problem changed many parts to get this far.but am learning more very quickly.
thanks