Help with another diagnosis?

[bohmankid]

Vehicle in question: 1985 gmc 2500 with 2001 5.3 vortec motor.
My truck is running crappy. When I floor it (or even go past half throttle) the truck bogs down and will not accelerate. If I accelerate slowly, it'll go.. just slowly.. When it's in park, I'll put the pedal to the metal and it will cut out at 3-4000 RPMS. (Sounds like a rev limiter at 3500 RPMS). I've tested the fuel pump and all fuel lines are fine. The check engine light never comes on. Spark plugs are brand new (started having these symptoms with old plugs, so it's not plugs). Suggestions?
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