My dads truck was acting up and had no power. I would press gas and rpm wouldn't go above 2000. I unbolted exhuast and it worked so we replaced the cats we thought were clogged. It worked good for a few days and then did the same thing again. Now it is backfiring through the air intake. Any ideas and fixes?

 

Plugs and wires OK?
Cap and Rotor?
Clogged injectors maybe?

 

Plugs and wires are a few months old. How do I know if cap and rotor is good? There is spark on all plugs and goes up in rpm when you gradually press gas but anything over 25 percent throttle it dies or loses power.

 

Sounds like a clogged fuel filter or bad fuel pump.