Does anyone make an engine management software that can control the 5.3LV8-V4 system (08) to be able to intermideately lock the engine into the V4 Mode when I wanted?

On flat land, the engine would get better mileage if I can keep it in the V4 mode than constantly switching between the V8-V4.

If there was a software program with a switch or something that could lock the engine in V4 mode when there is no load on the engine, I would be interested.

 

No and you don't want to do that, you will damage the motor.
The AFM system is programmed so that anytime shutting of half the cylinders will benefit it will do it automatically.
If under much of a load then the engine will actually get worse fuel economy if it were to switch into 4cyl mode.