So many of us have been where you are--overwhelmed and confused.  Know this--the DDT/E philosophy works!  All four aspects must be in place for the best results.  I have a couple of thoughts.

One, Diagnosis.  Since your vet did the DST to diagnose PPID, you don't really know for sure if IR is an issue for Rudy as well, but it looks highly suspicious for a couple of reasons.  A high ACTH can drive the insulin up causing IR as well.  Consequently, all PPID horses should be treated as though they are also IR until proven otherwise.  Like Mandy said, "avoid laminitis at all cost"!!  It will not hurt Rudy, even if he is not IR at baseline, to at least temporarily start the emergency diet, until you can get your vet on board with the recommended lab work, (ACTH, insulin, glucose and leptin on a NON-fasting horse).  Leptin resistance goes hand in hand with insulin resistance.  Leptin is the hormone that says "stop eating".  Your comment that Rudy has a voracious appetite and has gained weight, makes him very suspect to be insulin and leptin resistant, especially given that his PPID symptoms have been going on for "the past several years."

Here is the link to Cornell's website.  It's the lab that we recommend you send your blood work.  The bundled ACTH, insulin and leptin is $62 + $8 to add a glucose.  Ask your vet if he/she will do these particular tests for you.  They are explained in detail on our website, which Mandy gave you the link to.  He may (will) charge you more than what the actual cost is, but those 4 tests are what you need to know if you are dealing with only PPID or also IR at baseline as well.

https://ahdc.vet.cornell.edu/test/list.aspx?Species=7&Test_Name=acth&TstTyp=&WebDisc=

			https://ahdc.vet.cornell.edu/test/list.aspx?Species=7&Te...
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 I also see that your vet is giving you a 60 day supply of powdered pergolide.  Please know a couple of things.  The compounded powdered pergolide IN CAPSULES is what we recommend, but the powdered pergolide in a jar will help you with your initial weaning on to the drug.  Make sure you stir the powder up each time you dose as the medicine and the carrier can settle and separate, and stirring will help you get more accurate dosing.  The reason that we recommend the capsules is that each time you open the jar of powder the drug is exposed to humidity and light and that has a degrading effect on the medicine.  The capsules help preserve the integrity of the drug within.  Still, we recommend that you order only 30 days at a time and keep it in the door of the frig.  Here is one place that you can fill a prescription that your vet writes you for pergolide:  http://www.pethealthpharmacy.com/

You want to wean Rudy on to pergolide slowly to avoid the initial side effects that some but not all horses experience when starting onto the drug.  We call it the "pergolide veil" and the symptoms are depression and lack of appetite.  I know, it probably seems that Rudy could not possibly have a lack of appetite!  But it can be a sobering side effect if it does happen.  So you will want to start him with 0.25 mg/day for 3 or 4 days and increase the dose by 0.25mg every 3 or 4 days until he is at the target dose.  After at the target dose for 2 weeks we recommend retesting the ACTH to see if it is being controlled with the target dose.  There are also some other subtle symptoms that may help you and your vet decide if you are at the target dose.   Please read this scale of symptoms post from Patti:  https://groups.yahoo.com/neo/groups/EquineCushings/conversations/messages/111988  Another thing that can really help with the pergolide veil is a product called APF, available at some local tack and feed stores, online, and through their website:  http://www.auburnlabs.com/html/eqProdGen.html

Please take the time to join ECH8 and fill out the case history form on Rudy.  Mandy has sent you a link, and an invitation as well.  It really does give us the details we need to help you better.