'90 SC w/engine miss - builds normal 12# boost when you full throttle, but if you hold it there, it keeps climbing hits max on the boost gauge.

I checked the bypass and it's not hung up and works when you blip the throttle, hi-flo cats are 5 yr's old but only about 12k miles on them (110k on car), smells rich at idle, 12 mpg, O2 sensors are 6 months old - why does the boost keep climbing, even w/engine miss? Temp gun says both cats equal and they don't seem to be glowing.

Plan on doing head gaskets and injectors soon, but this runaway boost is new...what are common causes?