You know that Restore stuff that comes in a silver can? I added one of the eight cylinder cans plus one of the four cylinder cans (total about 20 ounces, the cylinders just refer to the size of the can) when I was low on oil just to see what would happen. It seems to have raised my engine vacuum enough that my vents always work properly regardless of speed etc. Also my cruise control now holds speed on inclines a lot better.

My truck has 123K easy miles and runs well. I never had a vacuum issue until moving to Colorado and living at 5,000 plus feet altitude. Even then it was not bad, the vents would switch over at highway speeds if I gave it oo much gas and the cruise had issues holding speed on inclines. But the Restore seems to have raised it enough to work properly here too. I didn't do anything else so it had to be the Restore.

I have never checked any of my vacuum system for leaks. I just sort of looked over the hoses and didn't see any obvious holes but I was not very thorough. I may have a leaky canister or something, I am going to buy a cheap vacuum tester to find out. But the raised engine vacuum is a big help.

QUESTION: Could I add an extra vacuum "coffee can" to each side, cut it in with a tee or something, to hold more stored vacuum? Would that work or cause problems?