Will a clogged cat do this???
 

I'm running the full non sequential set up now.After 8 hours of back aching work.I figured going to the full non sequential setup would cure my 5lb boost issue.But of course it did not.Now I'm thinking my cat and precat are clogged.I also have a small exhaust leak somewhere by the turbos.I cant find the exhaust leak though.

Second.if the car has not totally warmed up it will hit 10lbs once or twice then drop back to 5 or 6lbs. Will clogged cats lower your boost after they are warmed up?

I had a leak that was causing random 5-6lb boost. Turned out to be the coupler for the Y pipe and Crossover pipe. The lower of the two clamps was almost off, whenever I hit the throttle, it'd push itself off the Y pipe and leak almost all my boost. You could even watch it happen while the car was sitting.

Although, yours sounds a little different, it is something you could check.

Non seq will run fairly well with a cat but not with cat and pre-cat.

With a clogged cat the systems are: normal vacuum and low boost driveablity, but when you get on it hard, boost stays low.

It happened to me when the front brick in the cat broke up. Boost would not go over about 3-5psi. The exhaust was also quieter.