Why would your 92 Nissan pickup 4cyl 24 liter be very sluggish when accelerating even after you've changed the fuel filter air filter and added injector cleaner?

I had the same problem with 137,000 miles on my Nissan pickup. I replaced the spark plugs and the spark plug wires (with high quality ones). I bought a rotor and distributor cap, but did not replace them. I will in the near future. Just the added items made the truck run like brand new. Much more pickup.