97 Silverado vibrating accelerator @ 42-52mph

(Posted in wrong forum originally, reposting in (hopefully) correct forum now.. )

I searched through many postings and couldn't find another exactly related to this....

Recently bought a 97 silverado that's giving me a little vibration in the accelerator / gas pedal only between about 42-52mph. It's not during acceleration or during braking. Just when maintaining current speed. (I'm just barely pressing on the gas at that time).

If I speed up or slow down, it's gone. I've seen things about drive trains, greasing up grease points, air filter problems, dirty plugs, etc... But nothing conclusive. Before I go bringing her in for an unecessary tune up or getting the rear end replaced I thought I'd open it up to you guys..

I'm not a wrench, but would love to find a good answer to try myself or give the local wrench some educated pointers..

I'd appreciate an email to [email protected] and a reply to this thread so others can see the response...

THANKS

Couple of things come to mind-- Harmonic balancer bad--U-joint just starting to go out--Balance weight on driveshaft missing--Fan or fan clutch off balance or missing a piece-- Flex plate cracked--Please post again after you find out.

excessive dirt buildup on driveshaft can do it too.

no joke, i saw it in a chilton manual troubleshooting guide.

also, maybe its just the nature of the beast, like many older carbureted cars that shudder a little when you start from a red light

One other simple thing to check especially if the tires aren't brand new or it has aftermarket wheels: check the tire balance. Even though you are feeling the vibration through the accelerator pedal, a rear tire could be out of balance.
Simple way to eliminate this is to rotate the tires front to back. If one is out of whack you will feel the vibration differently (through steering and/or frame.)