4.0 cutting out........

[Broncopower33]

Ok, I have a 90 bronco II, with a 1991 4.0 explorer motor in it, and I am having a problem. Right around 45 55 mph the motor starts to cut out?? I put new "ford" spark plugs and wires hopping that would fix the problem. The cutting out only happens under load as in going up hills and stuff??? If anyone has any input that would be great.
Thanks:

 

[04sd]

fuel filter?

 

[Masterd]

Fuel filter or dirty injectors?

Possibly fuel pump.

 

[Broncopower33]

Fuel filter is new, and I did a fuel sys test, and I am under the 35-45psi. I think I was around 29psi? What about the valves being bad, I understand that Cylinder number 5 can cause problems??