L-98 Miss at Steady Speeds

My 89 L-98 has a miss when running at a steady speed, about 45mph is the worst.

When cold, it runs great but after a few minutes the miss developes and becomes more severe the hotter the engine gets.

Acceleration is flawless, not a miss, sputter or hesitation at all, only when driving at a steady speed. At idle it feels like a random cylinder not firing, no pattern at all.

So far I have replaced the plugs, plug wires, cap, rotor and coil. I suspect a fuel injector or two but really only a guess.

Any opinions?

Rick