Usually does not work well for me. If it's flat and calm, I leave OD on. In that condition, I need a steady foot to keep it from unlocking the converter.
But if it's windy or hilly enough for me to lock out OD, my particular vehicle locks out both 6th and 5th gears, forcing me to run in 4th. In that condition, as long as it's not to hilly, rpm is high enough to have adequate torque to keep the convertor locked, even with cruise in operation.
Either way, if I see or feel the trans hunting (or see the convertor slip gage jumping on the Scangage), I shut of cruise control.
thebrakeman ('70), DW ('71), DD ('99), DD ('01), DD ('05)
2004 Surveyor SV261T (UltraLite Bunkhouse Hybrid)
2006 Mercury Mountaineer V8 AWD Premier
Equal-i-zer WDH (10k), Prodigy Brake Controller