I think your right about the pluggeg exhaust. I have 5 ins of vac when the engine starts messin up w/ the throttle held down. and over 20 @ idle.. what is plugging the exhaust ? the cat.? It will rev up for a min. or so, when it first started & gets worse as it runs, it has tried to stall when i lift but has not as of yet. it has set of a code p0101 & p0300-random misfire, I would say because of it missing when it starts losing rpm. It will start and idle fine.
YES.. chances are it is the cat. THere have been some reported cases of the muffler being plugged up too.