code p0720 and p2106

Do you mean it shuts off when placed in a forward gear or that you put it into a different gear and it doesn't move? Does the engine misfire or bog down when in those gears? From the description I would say it is an internal transmission failure if the engine runs but no forward gears operate. The codes suggest that it isn't seeing the transmission parts moving when you select a forward gear and it goes into limp mode.
Quick question, does the speedometer register movement when in reverse? If it does it isn't the speed sensor.

It will stay running but will not move in forward gear. The speedometer will not work in reverse.

Okay, if no speedometer in reverse then it could be the output speed sensor causing the limp mode. However the lack of all forward gears still suggests the forward clutch assembly. If you manually shift into the other gears does it move then?

My F150 is doing the exact same thing!! Please help, what was the verdict on yours?

DCVOLCOM909, we never had a return reply about the issue in the original posters F-150. If yours is acting the same way you likely have the same issue but without testing it to be sure.

Thanks for the reply, I really wish this guy would've given his resolution. It is identical to my issue, but I replaced the Output Shaft Speed Sensor and it did not correct the problem. Also swapped the filter and fluid just in case, but I'm thinking the clutch for the forward gears is gone.

Very likely, If you manually select the gears and get nothing then it is rebuild time as it is internal. The speed sensor can be an issue but it's not as common as internal failure in this case.