Are they platinum, copper, etc.???

 

What brand sensors? If they aren't NTK, or Denso, take 'em back.

 

They were NTK. I also bought a fuel injection pressure tester so I dont have to keep renting one. The new pump is reading excellent. 62psi at idle. 55psi after priming key forward. Old pump had 0 psi while priming and 35psi at idle.
I think the plugs are platinum. Really small electrode as well.

 

These engines really don't like rare-earth plugs..... You get mystery misfires, and other odd performance problems......

 

I have heard similar with another v8 I was working on. But in this case I dont think it's the source of the problems.

 

Yup. Only copper spark plugs on these trucks.

 

Do you think the computer needs to be flashed at the dealer?

Would a programmer do the same thing without having to bring a rusty old truck to a new car dealer?

 

How old are your O2 sensors? They have the biggest impact fuel mileage.

 

I replaced the upstream sensors yesterday. They werent that old though.

 

JRsick and HEYOU. Advised me too run NGK V-Power plugs, With a set of
Taylor ThunderVolt 8.2 shorty plugwires. My 5.7 has a smoother idle, fuel mileageWent up to 16 mpg,, noticeable throttle response. I have the 9.25 corporate open rear diffIm very pleased. Hope this is a bit of help.