1998 I tried to quote your thread but the fracking adds covered the insert quote window....
That was my thoughts also on the tires going in and out of phase. The truck came with a "cheap" set of tires and one of them took 3 1/2 ounces to balance. The vibration can go on for 10 miles or more and disappear for one mile then come back again. Rounding curves doesn't seem to make much difference. I'm wondering if one is slightly out of round????
It's just a goofy thing. My gut tells me it's tire related but I'm going to check that driveshaft angle also.
Thanks everybody for all the input. Oh the joys of owning a 32 year old vehicle!
Ken