Actualy it should feel like a gear after 4th...
Should shift...1-2, 2-3, 3-4...and over xx mph, at xx accelerator pedal %...lockup.
Pulling a hill in OD, convertor locked...with cruise on...the engine is well under its power band, so it begins to lose forward speed..the cruise compensates by increasing accelerator input...if the engine is unable to stop the loss of speed, it will unlock the convertor....if towing (and you shouldnt be towing in OD anywats, but..if you are) it will drop the lockup, and downshift to 3rd....to let the engine rev.