my '05 Explorer loses air vent pressure when I accelerate, with a/c or just vent air. Will blow out the floorboard area until no longer accelerating. What can be causing this problem?

Does the speed of the blower fan sound like it's slowing when you accelerate? Or does it remain blowing at the same speed and only the vent direction changes? (ie it shifts from dash to floor). If it's shifting where the air blows from, check the operation of the EATC if you have that option (it's a computer module that governs AC and blend and mode door operations). If, however, it feels like the blower fan is "bogging" down, you may have an undervoltage problem, which could indicate a failing alternator. Take it up to any parts store (Autozone, Advance, O'Reilly) and have a them do their free charging system check.

Losing vacuum either from control panel or the junction splice or in the engine compartment. Check vacuum hoses and also one way check valve. Follow vacuum line in engine compartment and you'll find check valve