Throttle

Your description sounds like it has something like a throttle commander installed, that is exactly how those work. They basically trick the ECU into thinking you are pushing the pedal farther and faster than you really are. So you step down slightly and it doubles that. Most of them are plug in devices that go between the throttle pedal connections and have a control box. The throttle is fully electronic on that van and isn't adjustable that way unless you go into the coding and rewrite it. The pedal is basically two potentiometers that operate independently and in reverse of each other. They have two 5 volt sources and two grounds and one raise the voltage while the other lowers it, the PCM uses both to determine throttle input. It will also trigger a light if there is a problem. Probably the first thing would be to use a scan tool and see if the pedal inputs are correct. It would read a percentage and the voltages the pedal has to it, you would be looking to see if the pedal showed say 7 volts instead of 5 or that pressing half way reads over 50 percent throttle.

Did this just start happening or is this a recent purchase that is acting strange?

Any good shop that you trust should be able to look it over and give you a solution, It might just be one with a "touchy" pedal. I get an Equinox in now and then like that, bone stock but if you breath on the pedal the engine revs up!

Don't really know of a shop out that way that does automotive diagnostics, there are quite a few parts cannon shops though. You might ask on facebook or other social media, or see if you can get Mustie1 on you tube to give you a pointer, he is a decent guy who is in Plaistow, he might know of a good independent shop.