Chevy truck problems

I have a 1988 Chevy step side 305v8 4x4 single cab. I've had this truck since I was 14 and never had this problem and couldn't figure it out myself. It wants to hesitate on take off and spit and sputter. I've always done regular maintenance to it. It just started doin this. I've changed the plugs,cap,rotor,throttle position sencer, and air flow sencer. And the plug wires are only about a year old. She's got 235xxx miles on her now and she still runs great other than this issue. And when I go to kick down a gear to pass it fall on its face befor it actually starts to move and even when it does start to go its not as much power as it used to be. I do beleave it has a jasper engine in it it's not the stock engine and the sereal number has an h.o in it and I'm told that means its a high output engine. The only thing I could think of to replace would be the map sencer or coil. I need someone to help me befor I put more wasted money into it I'm tired of the guessing game this is my last resort. Thank you for any advice  

It's either spark or fuel related...If I had to guess, I'd say fuel. Is the filter fresh. Is the fuel stale or old/water in it? Is the fuel pump in good shape? Does it only run sluggish at higher RPMs and under heavy load?  
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John Cappa
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