Vibration under load

I have a severe vibration that started as faint and somewhat annoying, showing up mostly when the engine was under load (long hills, heavy acceleration). It's progressed to the point where it's very noticeable, still mostly under load. I can feel it in the dash and see the vibration (fuzzy mirrrors). I don't see or feel this when the car is stationary with the engine running. Any thoughts?

How many miles. What year and model? Also what speed? How does it feel when the car shifts?
Thanks
http://img.photobucket.com/albums/v425/kustomkid54/1998PontiacGrandPrixGTP004.jpg

2001 GTP, 80 K on the car, rebuilt engine, appx 15 K on that. Shifting is ok, vibration is extreme. I noticed that when were driving up a long hill and we hit a small bump the vibration seemed to change or stop for a second, then resumed again. :banghead:

P.S. It more noticeable over 30 mph. The weird thing is that it's not noticeable unless the car is moving, never at idle or if I raise the RPM while it's sitting still.

if not misfiring maby broken motor or tranny mount i think those and gel filled mounts ?

I would have the CV axles and motor/trans mounts checked, could possibly be a bad hub bearing too, as they can act up only under a load.

Thanks for the reply. It's weird, but it seems to me that the vibration is more noticeable as the car warms up.

I think it's the CV joint(s). I was working on the car yesterday (replacing S.C. belt tensioner) and noticed a line of grease that looks like it sprayed up from somewhere near the outer right cv boot, like someone took a spray can and shot grease in a straight line from that point up the firewall and up onto the hood blanket.

Sounds like the CV joint/s and the boot is bad and let out all that nasty green grease all over.Maybe time to replace CV joints and get some good boots from Zommer @ zzperformance.com

http://www.zzperformance.com/zzp/products/suspension/rockford_cv_duraboot.htm

http://www.zzperformance.com/images/prod/suspension/rockford_cv_boot.jpg

A sure sign of failure on your stock CV boot is green grease under or around the axle. Installing an upgraded boot will replace your worn boot or give you the added peace of mind from running the best. Rockford's Duraboot (inner boot) is made of a Monsanto blend of special thermoplastic materials which resists temperatures from a frigid low of -65 F up to a scorching high of +475 F. The Duraboot is the ultimate joint protection against variable operating temperatures and destructive road abrasion.

~Larry~

I have the same problem I took mine in to a local Exaust and tire specialist they could not find the problem They look at me as if nothings wrong but I feel it when I accelerate and now im feeling it in the steering wheel. Let me know what you find.

I've got the same problem. It even feels like warped disks at times and then other times the brakes are flawless.
When driving down the highway at 60-70 mph the steering wheel shutters and when I hit any good incline you can really notice it get worse.