Hi Andrew, I'm Tracy G in Reno Nev. I'm still a fairly new Gadgetman, but let me see if I can give a few ideas...First your Grooves look great in that Ford TB! Nice work there, along w/ the IAC gasket of metal tape ya made. Remember to aggressively check for any possible vacuum leaks, example that vac. hose on the TB bottom looked pretty pale.
Anything that is connected to vacuum below the throttle plate is to be considered Guilty untill proven OK. Replace any old vac hoses--if hard/ rotten don't cut 'em back, REPLACE 'em! Does the TB itself have a good seal to intake? Manifold gaskets need checked, try spraying w/ a little carb clean at idle listen for idle speed reactions. Things you might not think of like power brake hose, any vacuum hose tee's, again ANYTHING connected to manifold vacuum below throttle plate all the way to manifold to head gaskets needs checked (sorry I know the manifold gaskets on that van aren't any fun but if original...
A Mityvac or similar vacuum hand pump is invaluable for doing these checks. You cut nice Grooves on this puppy and they are creating a spike in manifold vac on the intake stroke--they HAVE to 'cause of the Power increase you are seeing. The Vac Spike makes any vacuum leak worse and the leaks all need fixed to get full potential of the Groove(s).
How many miles on your van? Many tech's say that O2 sensors can't be trusted past 60 K miles. Is the check engine light staying off? The Groove isn't a cure all for other issues. Forget the Groove for a moment--think of the issues that affect fuel economy. If you need a tune up add 20% to the plug gap, re-gap the plugs anyway if they are OK. Cap/rotor/wires (I've had great experience w/ Borg-Warner Nascar Select ignition parts at Pep boys, O'Reilly, etc. done dozens of tune jobs w/ those). Tire pressure, filters, it all matters.
After all of that, did you do a computer re-learn on this van? You pull both battery cables(pull Negative first reconnect last) then connect both cables w/ jumper wire turn key on to run position headlight switch on, this drains power out of tiny capacitors in computer and dumps "learned memory". Leave like this at least an hour, turn key/lights off then reconnect cables. You then do the Re-learn for the van computer its described in detail elsewhere in Groovy Service bulletins and in posts.
The PCV re-route did you cap the Vac. port on intake manifold that PCV originally went to then route or tee the PCV hose into the breather hose from the air filter ass'y to the opposite valve cover? Been lots of confusion on that one, again look around the site its described in words and pics. It cant be cold in NM now is water under oil cap mix w/ oil? Check Radiator cap (cold) is any gook there? Hope not!!
I hope those ideas help, Andrew, glad you are back! Others can chime in here too..........
TracyG Gadgetman Reno