My 1989 Chevy Silverado 2500 vibrating when running, it is worse when driving

Start by checking the bulbs and the sockets and the wiring. look for discoloration and bare/ cracked wires. Fix or replace as necesary.

There should be an aldl (assembly line data link) plug under the drivers side of the dash. Ground the A and B terminals and turn the key to the run position. Count the number of times the check engine light flashes.

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usualy in the dash they are brown and green however the best solution is to run all new speaker wires

here you are my friend. Now i went way out of my way for this so i hope this is what you are asking for :)

check the switch u can do this by pulling the dash panel off and looking behind the switch check and see if the plug is conected if it is it may need replaceing

You didn't mention fuel filter in your list. That would be the first thing to change.

should hold roughly 8 quarts with the converter still full. Run the trans through the gears to get it warm, then check the dipstick while running. I would bet its still low.

under the dash and directly behind the fuse panel

Rods 45 mains 75...You have to look at the bearings and also use plasti-gage to check clearances and wear.

Try checking for vaccum leaks, use carb cleaner and spray it around the base of carb, vaccum hoses, edges of intake manifold, take pliers and squeeze the big line to brake power booster & see if it changes, pull the pcv valve out and cover with your finger see if it changes idle.