biscaynekid

Try grounding the lug.

Good possibility it’s the ignition control module. ICM controls the opening and closing of the injectors. It’s located on passenger side on coil mount plate. Black with electrical connector. Air box and hose removal makes it easy to get to.

I would still check to see if vibration stops while coasting in Neutral. This releases tension on drive train. If it goes away, I would check rubber mounts for tranny, drive shaft , ect. If vibration continues in Neutral , again, I would check tires/wheels, drive shaft. If you have a stabilizer shock absorber going from body to frame, check that too.

By ‘coast’ are you in Neutral? If not, build up speed then coast in Neutral. If vibration is there, I would check wheels/tires and possibly bent drive shaft.

Try disabling the alternator. Start truck and see if problem goes away.

I had a plug with the porcelain insulator cracked in two. It looked fine to the naked eye. It was sliding up and down the electrode, sometime blocking the spark. I was putting the plug back in the engine when I heard a clink. I shook the plug and could hear the clink easily .Pure luck finding it. That was causing my intermittent misfires. Even though you replaced distributor cap, the new cap could have a hidden crack causing a crossfire. Good luck

Check for vacuum leaks in hoses, pcv, brake vacuum booster(power brakes). Booster check: put in neutral and pump brakes. Does idle change? Also, if A/C is on, your idle is supposed to increase. If not, idle will be too low.

If the truck hydro-locked, it means water is getting into a cylinder as well as leaking externally. You can’t compress water. You will see white smoke coming out the tail pipe too. You’ve replaced the intake so the head would be most likely source. You could try head sealer additive to buy some time. Research to see which one folks have had good luck with.

PS: The side terminal batteries have a small bolt running through multiple ‘star’ terminals. They tend to get this black corrosion more so than top terminals.

Multi-layer wires connected to battery terminals will get black after a time. This black can cause intermittent connection. The starter wire to battery can still be good and turn the engine over, but if the wire going from the same terminal of the battery to the engine fuse/relay box is corroded and making poor connection it could cause the problem. Remove and clean all your battery connections. Good luck

Still absolutely no ticking/tapping. Here's an interesting link: https://www.mccluskeychevrolet.com/benefits-to-sticking-with-conventional-motor-oil/

I have 215,000 miles on my truck...owned it since 81,000 miles. Truck has always run quiet...I mean absolutely no valve tap at start up or after warm up. Never any serious problems. I have used 5w30 Conventional oil...always. Well, after being prodded to 'do it', I switched to Full Synthetic 5w30. No problem for awhile. Then, about 4,000 miles into my synthetic oil change I started to hear, very faint, valve tap at start up. It would quickly go away. I paid more attention as the miles went on. I noticed the valve tap was lasting longer before it quiet down. I checked my oil level, it was fine. I did noticed slight condensation and a yellowish tint on the rim of the oil filler cap and on the walls of the oil filler tube. Dipstick was clean. Well, I asked myself why all of a sudden am I noticing these little things. I decided the only thing I had done was switch oil. I decided to go back to Conventional oil, but not all the way. I switched to 'Synthetic Blend'. All was well 2,000 miles into the 'blend' oil change, including the condensation on the oil filler cap and oil filler tube. Five days ago I started the truck up in the morning. Valve/lifter tap was LOUD. Oil pressure was good(45-50). After a minute the noise went away. I drove to work and all was quiet. I completed my work day and got in the truck. I cranked it up and terrible Valve/lifter tapping. I sat there idling about 2 minutes...got a bit quieter, but still noisy. I headed home. A mile down the road all noise went away and stayed away. I stopped on the way home and bought Conventional Oil. I changed the oil and filter. I am all conventional oil now. The truck made a very slight tap on the first start up, but hasn't made a peep since. It sat over the weekend form Friday until Monday morning. I cranked it Monday morning and absolutely no tap or noise. I'm sticking with what's given me reliability for 215,000 miles.