I had the same problem.. anytime I was doing freeway speeds.... I replaced the blades with some costly rubber. I replaced the wiper arm... still nothing.. When I was at the West Coast Nationals I saw a guy there with a small wing on the driver's side blade so I talked to him about it. It solves this problem... what can I say... I hear Motorsports have them... The wing is about 5-6 inches long, and 1 inch wide at the widest point. It looked good too.
same solution as dennis. I put some wingies on the wipers and it keeps the wipers pretty much planted up to 125...
got mine in Japan, though, and they have these neat stand-offs so the wipers don't rest on the windows all the time. You manually set them up on the stands (attached to the wiper itself) after you park the car, and when you turn the wipers on, a speing pops the stands out of the way so they work normally. If anybody has seen these wipers here in the USA, or has a line for them, LET ME KNOW! I love these things! Makes the wiper rubbers last FOREVER without streaking!
i bought a set of "airfoil" wiper bodies and teflon coated blades at an autoparts store. I think they are Anco. The bodies have a small curved plate on each body near the wiper arm attach point.
The setup has eliminate all shake and skip, even in heavy northwest rains at 80! Yeah, I know, too fast.
The springs holding the blade to the window may be weak. I took some off my parts car and changed them and had a much cleaner wipe. The motor on my 77 is weak though and stops erratically. At least they work, I drove an old Nova for a while with no wipers, thank god for RainX.