My Suburban has been exhibiting the symptom of downshifting out of O/D, then upshifting again all while cruising at a steady speed on the highway, for about 3 months. No pattern to it other than the steady rate of speed and 10-15 minutes of driving. The frequency of incidents has been more noticeable lately. I had my mechanic check for codes (found none) and test the TPS (checked out fine). On a hunch, I added a second ground strap from the intake manifold stud where the ground cable from the battery attaches, to the frame rail. First time after the TPS check and ground strap addition, that I drove under those conditions (40 mile round trip), I had no problems. Living/working in the city I don't have regular repetition of that trip more than once a week, so I haven't been able to duplicate it yet. Would simply disturbing the TPS to test it or adding the ground be expected to solve the problem?