On a Thanksgiving get away. While getting on the interstate on an uphill ramp the tranny downshifted, I was going 70 mph at about 4000 rpm hit the cruise control and it never up shifted. Pulled of the next exit to check the fluid level it was OK. Getting back on the highway it seems like it is running in 2nd gear. Any ideas? The transmission was rebuilt about 20,000 miles ago due to failed lines.