My 98 4.3 will start instantly and idle, but try to give it gas and it bogs down. It'll rev to maybe 1500 and no more. Before I started wrenching, I was wondering if anyone had any ideas where to start. I'm thinking fuel filter or maybe plugged cat? Thanks in advance for any ideas!

 

pull a O2 sensor out-forward of the cat and see if that improves your situation. Jerry PS fuel filter-as you stated is another possibility. If not done in recent memory may be worth trying.