Can you continue to drive for more than a mile or two when it's acting up? If the brakes were dragging enough to keep you at or under 20mph and 2500RPM in first gear you would be using a whole lot of the go pedal and after a mile or two the brakes would fade and you would be able to accelerate again (albeit irresponsibly since you would have no real braking power). Also, when you release the accelerator the van would come to a rather quick stop.
Since you didn't mention either of these I'd say the hot brakes, while interesting, are not the cause here. Perhaps after we get it running right they would be worth looking into.
It doesn't sound like the catalytic converter but it is hard to totally rule that one out.
Since your van is an 06 it should have the fuel injection harness routed out the passenger side of the engine instead of the driver's side. I've never seen that harness fail, only the one that runs out the driver's side and WAY too close to the exhaust.
You mentioned the engine won't rev above 2500rpm when it is giving you trouble and you are trying to drive. When it is in this state, what happens if you put it in neutral and try to rev it? Will it also stop at 2500RPM? That would rule out quite a lot of other things.
My thoughts are that it is something electric or engine control related - perhaps a sensor or ignition issue. Have you checked the spark plug wires? Perhaps the coils heat up and start to short internally?
When it won't rev above 2500, does it run up that far easily then act like there is a 2500rpm rev limiter, or does it start to lose power and slowly climb to 2500 as you stomp on the accelerator?
If you get it up to 2500rpm then lift off the pedal and convince it to upshift, can you get to that engine speed again in 2nd gear, or does it never shift?