'06 Ford Freestar losing power

My '06 Freestar is losing power on acceleration (usually when going uphill). The RPMs drop to zero, the battery light comes on, and the red security system light on the dashboard lights up for a few seconds (usually only flashes when van is off). As soon as I release the gas pedal the power comes back. This tends to happen a lot around 75-80 km/h when the van is shifting gears (but not always at this speed). There is also a knock or ping sometimes when this happens (a mechanic friend of mine was with me one time and described it as a backfire). On a few occassions the van wouldn't start in the driveway (would turn over) and then started again later on.