Bad IMRC or ???
 

Have a 2000 Windstar and it has recently started bucking/shaking at around 30 mph and 40 mph... if I give it gas and get over 45 it never happens and if I give the gas a good shot during the bucking/shaking it typically resolves it unless I just go lightly on the gas and it eventually stops after it accelerates a couple mph or so. Also I could be wrong... but it seems to be worse now that the temperatures are warmer in comparison to during the colder winter months.

Bad IMRC or maybe something else?

So I removed the vacuum line from my EGR valve and plugged it with a screw and it runs smooth as silk... would this test mean it's a bad EGR or could it also be a bad solenoid?

Is it the 3.8L engine?
Do you have any trouble codes?
One common area of trouble with these engines is the grommets for the isolator bolts. They deteriorate and allow for vacuum leaks. The original ones were made of black rubber, the new ones are green and oil resistant.
Another one is the DPFE valve. There are 2 types. One of them is made from metal and it will corrode inside and the newer one is made of resin and works well.
The EGR ports may be clogged up and or the EGR valve may not close properly.
Looking for vacuum leaks should be high on your list.
The older IMRC are operated with vacuum motors and they are notorious for failing. The newer controllers are electrical and very reliable. However there are 4 small white plastic grommets on the links from the controllers to the butterfly axles. These plastic pieces get brittle and get lost. That will make the engine run a little rougher than normal but not as bad as you describe yours.