Vibration at 90km / 50 mh

Can anyone tell me if they had any problems with short spuratic bursts of vibrations while going at speeds of access of or around 90 km / 50 mh. At times the steering wheel vibrates hard and other times very lightly. This vibration doesnt last for more than 2 seconds and doesnt happen all the time. Im hoping only U-joints and not tranny work
The truck is a 93 chevy c/k 1500 5.7
Thanks

I would think that if it was the trans that it would be more RPM related. R u positive that it isn't tire/wheel? That would probably be better on your wallet, but I guess you can't pick the broken part :)