Why after putting a new battery in my 2004 Explorer, did I loose my gas pedal???? Will not accelerate!!

Long shot here...

Could the throttle position sensor (TPS) connector have been removed or knocked loose from the sensor at the end of the throttle shaft? What about the throttle cable on the opposite side of the throttle? And for the longest shot, could the connector on the engine control module be partially dislodged?

Other than that it get's more complicated like a bad TPS sensor. If you have a meter handy one lead of the sensor will have a fixed positive voltage the opposite lead will be ground and the center should vary from 0 (ground) to the voltage on the positive end as you increase the throttle. It works like the old amplifier volume control in a way.

I assume your issue is that the engine won't rev up when you press on the gas pedal while in park. If not then we will need more specifics on your symptom. You could always try disconnecting the negative side of the new battery for maybe 15 seconds and reconnect to see if the system works with a fresh restart.

Try resetting the ECM using a scan tool