Can someone please help me

I have a 1990 chevy truck with a 350.. i've been dealing with this miss forever i have sent it to the shop and it ran good for a few monthes then back to the samething.. i have replaced the distributor, cap, rotor, plugs throttle body.. The last time around after changing the throttle body it ran good with still a slit miss after i drove it for a while the miss returned.. changed the throttle body again miss was still apparent. so decided to check the plug when i removed the plugs the number 7 and 8 plug where both a little wet 7 more then 8.. the truck seems to run fine without load and at higher rpm's it runs great just seems to be at lower speeds and idle

could be a flat lobe maybe a collapsed lifter.seems like you have ruled out all the quick fixes unfortunately you may have to really get your hands dirty.

Thanxz okie-chevy-man that was actually my next thought to take a compression test just wonder if there where any other idea lol.. but i kind of figured not just looken for imput so i thank u very much for ur response

Did you replace the plug wires?

yes i replace it all did a tune up already

If your problem is intermittent you can rule out all internal engine stuff except valves and guides!
Unless your problem reapears at high RPM in en-which case maybe a broken piston ring.

Also you might try strobbing your ignition wires (all 8) with an inductive clip timing light, this will show you an intermittent ignition problem, keep in mind a bad or fouled plug will give you the same indication, take your time.

This could be a simple sticking valve!

-Mike