My car (stock 84 SE) seems to fall flat on its face around 5k-5.5k
Ive checked the 5th and 6th ports, changed the plugs, wires, cap & rotor, and althjough it runs better up until 5k it still looses power.
Im gonna do the fuel filter and O2 sensor tomorrow but any other suggestions would be apprecated, maybe clogged cats?
-Greg

 

Try driving around a bit at higher RPM's and take a look underneath the car to see if the cats are glowing at all? if they are, they are clogged.

 

check to make sure your secondary "choke" throttles are opening when the car is warm, its common for the vacuum thermo valve to fail

mike