snook,
I recently went through a similar debug on my 85 and I think I have a pretty good handle on the workings of the system. When I took my EGR switchover valve and ARV valve out, I had flaring too. The ARV valve leaked badly, and a past tech must have adjusted the VCV to compensate for it. It shifted great WITH the leaky valve. Once that valve was gone - flaring. I was at about 13 mmHG when I was getting the flaring. I went down to about 8 mmHG at idle by VCV adjustment and the car shifts wonderfully.
*Your next step is to adjust the VCV to give you less vacuum at idle* You need an 8mm little wrench. There is a plastic cap on the VCV itself, its small and points to the driver's side shock tower. Pull that off, you will see a brass adjustment piece with 8mm flats. T your gauge into the line that dives down to the vacuum modulator (the black line that goes down behind the engine to the transmission area). Start the car. You will read something on the gauge. Turn the brass adjustment piece clockwise for more vacuum, counter clockwise for less. You will want LESS. You will probably need about a 1/4 turn to get down to the 8 mmHg range. (tip: hold the rack while you are making adjustments, or it will want to rev the engine - youll see what I mean) Set it there, remove the gauge, go for a drive and see where you are at. You can make micro adjustments one way or another without the gauge if you need to fine tune.
Its far easier to adjust the VCV than the blue flying saucer. Go that route. Try to remove the saucer to get at the adjustment and you'll see what I mean.
The top switchover valve behind the brake booster is a temp switch to allow for softer shifting when the engine is cold. Its a nice feature. My 82 shifts more harshly when cold. The 85 definitely adjusts accordingly and it's nice - don't eliminate that feature unless you can find a fault.
Hands off the spring kit till you have exhausted the possibilities here
This process is so delightfully easier.
dd