runs good then looses power
car runs good for about 5 miles, then looses power and has high RPM's and warning bells go off,car can sit for about 20 minutes, then it runs good again for about 5 miles and back to no power (changed the EGR valve, fuel pressure valve, air filter, and fuel filter)
Is it over heating? If you can't figure it out join www.cadillacforums.com There is so much information there it is crazy.
replace the catalytic converter, it had started to come appart, that should fix the problem.
If the catalytic converter is on its way out, the exhaust should smell like rotten eggs, or sulfur. I don't think the high RMP's can be related to a catalytic converter, but I'm unsure.
possibly a transmission issue , if it revs up and goes nowhere after 5 minutes. The trans filter could be plugged and cause oil starvation and in turn cause a slipping transmission ( hi revs and no go ), or it could be internal seals and /or clutches slipping when car warms up.
Like some people said before could be your catlytic converter depending on the smell also take the oil cap off and feel how much back pressure is coming out