Ok, I have one question. How much intake manifold vacuum does that engine create with that roller cam?
Don't know the answer to your Q about the intake vacuum. Not a mechanic. Have one doing work for me.
On that proportioning valve. The plunger has to be centered in order for the brake warning light to work properly, if not the light will always be on. To center it, if you have to you just open the opposite bleeder from the last one you bled and press the brake down untill the light goes out then tighten the bleeder.
The reason I asked about whether you have bled brakes or not is because if you let up on that brake pedal any at all while any of those bleeders are open you will suck in air.
My sincerest apologies to you "heavy chevy 396", for taking so long to respond to your latest answer. I've been mulling over, in my mind, all the answers you've given me up to this point, and everything you have suggested has already been tried and tested.......I STILL THINK that I will try putting the original Prop. Valve back on and check it for CENTER positioning. The loose wire connection that I was telling you about fits the connector on the original Prop. Valve to a "T". Once all that is done, and if it still doesn't work, then I don't know WHAT I'll do next....one things for sure though...I'm NOT getting rid of my truck.
Even though this matter is yet to be resolved, I am going to accept your answer, as I do not wish to take up anymore of your time....Again, I'm sorry for the delay, and whenever we DO resolve this issue, I will log onto this site and leave a message for you, explaining what our findings were....just in case the answer may be beneficial to you.