would using 10W40 in a 2000 Plymouth Voyager minivan 6 cylinder cause it to lose oil pressure.

nope, when you lose oil pressure its usually the pickup tube is clogged, or the pump is about to fail.

Most modern engines have much tighter tolerances/ internal clearances, & as such, a thinner oil is recommended by the manufacturer. The most common weights in use today r 5w-20, 5w-30, & 10w-30. 15w-40 is also still an old standby for diesels.
10w-40 is likely a lot heavier than what is called for, but making that change alone should NOT cause an engine to lose oil pressure. Is there any actual noise coming from the engine, or is there just an idiot light/ gauge that is telling u the pressure is low? If there is no noise (tapping, bearing/ rod knock), then it is possibly just a faulty sending unit for the gauge/ light.
If there IS noise present, then a physical problem is suggested.. a weak oil pump may not be able to create enough draw/ suction to get the heavier oil up into the engine, hence the low pressure reading. The bad news about this scenario is, once the noise has become apparent, the damage to the engine is irreversible.

before people get crazy on oil weights,see if your sending unit is bad,or guage,oil pressure is not going to drop because of 10/40

It might cause the engine to knock on startup, seeming like low pressure. It is too thick to get where it needs to be quickly. Your manual says 5w30, pretty much all year round, unless you're in extreme conditions. 5w30 gets everywhere quickly, and wo not cause knocking on startup.
Also, Fram oil filters can have bad check valves that let oil drain back, causing startup knock.

next time buy Mobile5w-30w