96 crown vic engine trouble

1996 ford crown victoria 4.6l 160k. hard starting when outside temp is below 40. there is a hesitation on acceleration, the harder you stab it the more it cuts out. sometimes any amount of gas you give it makes it want to drown out, but it will idle its way just fine up to 35mph. sometimes at 65mph it begins to lose speed and the motor makes no power, the more gas you give it the worse it acts.

When was the last time it had a tune-up?

When was the last time the fuel filter was changed, if ever?
Clogged filter leading to low fuel volume can cause this.
A failing fuel pump (often caused by a clogged filter) can also do it.

The mass airflow sensor was malfunctioning.

That’s what I was going to suggest next! Shucks! Somebody beat me to it.
I’m glad you changed the fuel filter, just in case. I’m sure your mechanic checked the functioning of the throttle position sensor, the engine coolant temperature sensor, and the idle air control valve. I know he wouldn’t wildly throw an expensive MAF at the problem, and that he used an MAF cleaner, first (which didn’t improve its output signal).
Thanks for posting the resolution you found.