05 4.0 loss of power

Slightly warmer than normal. 195 thermostat and it’s running about 210

You need to find out if the reason the upstream cats were replaced is because they failed and broke up the catalyst. Typically when that happens, the pieces move down and block the main cat which then results in a gradual loss of power until it will not run at speed.
  • Like
Reactions: John Cooper
Even though the upstream cats have been replaced roughly 10k miles ago, it seems like they are bad again. I pulled all 4 O2 sensors out and went for a ride and got some power back. Not sure why they failed again but it is what it is. Thank you everyone for your help and input! Glad to have found this forum!
Most likely the mini cats clogged the third cat on the skid when they failed.

If the mini cats actually failed again, you need to fix the misfire/rich condition that is killing them.