93 Shortbed 350 TBI Weird Shudder at idle/oscillation when warmed up.

[Bosco2023]

Hello, 2 weeks ago I bought a 93 Silverado shortbed 2wd auto with the 350 tbi engine. After taking longer trips as I build more confidence in the truck I've noticed that when pulling away from a stop light or even revving the engine in idle that the truck had an oscillation that grows with rpm. Not an engine miss but feels like an unbalanced driveshaft feel even when not moving. Plugs, rotor, cap and wires are new. Tranny fluid is fresh, and oil pressure seems fine. It has about 60k on the jasper engine and has the same on the jasper trans. I noticed also that the clutch fan is pretty loud even when warmed up. Balancer looks good and looks aligned properly and has no wobble. First 10-15 mins of driving is normal but when engine and tranny is up to temp, it starts acting that way. Ive even put it in neutral while on interstate at speed and rev it and can feel it. Can it be tq convertor bolts? I know the previous owner did a few small mods to the truck cause the tranny shifts hard enough to chirp a tire under medium throttle. Just didn't know if it sounds like the clutch fan, convertor or ect.

Thank You for all the help
Rich

[Bosco2023]

Turned out to be a bad ignition coil