Help! Vibration at 80mph and above

[Morpheus53]

Hey everyone. I have searched and searched for a problem like mine but can't seem to find any info. I have an 85 c4 and have put a tremec tko-500 in it. I just upgraded to a Ram stage 2 clutch and haven't driven the car for about 4 years. Was unable to do the work due to back issues. Anyway I final got it back on the road and have a pulsing vibration that starts at 80mph and gets worse if I go any faster. I have checked tire pressures and looks like all my balance weights are on the tires. Also all of the u joints seem to be tight and no play. Also the rear dif oil looks great. What could be the cause? Thanks for any input

 

[GWinter]

have you checked wheel bearings ? Sitting for four yrs tires could have flat spots that could take awhile to correct themselves , also how old are the tires age could be a problem..

 

[Morpheus53]

have you checked wheel bearings ? Sitting for four yrs tires could have flat spots that could take awhile to correct themselves , also how old are the tires age could be a problem..

I did shcek wheel bearings. No movement and I haven't heard any noise. Plus it doesnt change from side to side. I have been thinking about the tires but usually that is a consistent vibration that sticks around a certain speed. They are 15 yrs old. I just replaced a u joint on the drive shaft that seemed to have a flat spot which was only noticeable after I pulled it and tried to move it back and forth. If that doesnt fix it then I will start messing with tires. Thanks