87 bronco lacks power uphill

My 87 fullsize 5.8L recently stopped performing as well driving up hills. I can feel the power leaving as I start going uphill, just like my old 4 cyl wrangler with too big of tires. anybody have any idea what the problem might be? there is no pinging/knocking noise. Fuel pump or filter maybe?

Cat. convertor maybe. Do you have a lift, or big tires or anything like that?