88 Ranger misses after getting hot

[Pj10442]

My 88 Ranger 2.9 v6 runs fine when I first crank it but after it gets warmed up it starts missing like it drops 1 or 2 cylinders. I have also noticed that when this happens and I press in the clutch to change gears the rpms shoot up by approx. 500. I have replaced the dist. cap plug wires rotor button and plugs any advice before I lose my mind???

[Elizabeth0365]

try replacing the O2 sensor. The porcelain part of it may be cracked or damaged.