[Slade901]

Update, after changing the oil and oil filter, it seems the vehicle is barely able to move 15MPH. I can't do 40MPH anymore. I can definitely hear a lot of air escaping when I rev the engine.

Here's what I'm puzzled, the engine idles great. My plan would be to remove the O2 sensor and try to drive around the block to see the engine will have more power and go past 40MPH. I could get a back pressure gauge but that will take a while. I need it to try to narrow down the problem before I take it to a mechanic.

Either I have a clogged cat. - Possible
Bad intake gasket - not sure because the engine idles ok.
Bad plenum gasket - not sure because the engine idles ok.
Bad head gasket - not sure because when I changed oil, it was not milky.
Broken valve either intake or exhaust - not sure because I don't hear tapping noise.