jd512k

Hi all. Brand new memeber here. Just bought a '90 Silverado, 350 auto. Have replaced all fluids, filters, PCV, & plugs. Had a new flowmaster installed yesterday, and have run fuel system cleaner through.. It's running pretty rough from off idle to ~2000/2500 rpm (No tack, so I'm guessing on the rpms)... then purrs like a kitten, from there on up..

There's no popping from the exhaust to speak of.. just a noticeable, rough running vibration from the motor.. strong enough I can feel it through the floor, steering wheel & seat.. and see it in the mirrors..

[align=left]Any suggestions on where to start looking would be greatly appreciated!
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Thanks!
JD