A friend has a 1998 Mazda 626, 4-cylinder, automatic transmission, 140,000 miles. Transmission was rebuilt about 30,000 miles back. The problem is that after you have driven on the highway for about 150 miles, the transmission shifts become almost violent. If you slow down to around 60 mph for 30 minutes, it goes back to normal for a while. They installed an auxilliary cooler when the transmission was rebuilt. It seems to work fine around town. Fluid is full and seems to be in good condition. Any ideas?