1996 Chevy C1500 bad acceleration

Hello, I have 1996 chevy c1500 pickup with about 148,000 miles on it. It has a 4.3L V6 engine. Lately its been acting weird. Whenever I go to accelerate or go up a hill it acts like its not getting any gas. If I floor it, the engine won't rev past 2500 rpms. But if its sitting still it'll rev past tht just fine. I've already replaced the fuel filter, fuel pump, and just put in new spark plugs. I had someone scan it with a scan tool and the only codes that came up were one about the #3 cylinder misfiring and something about an error in the computer that controls the transmission. Any help would great!