You may as well put that car on blocks for long term storage. You keep shooting down every idea.......yet YOU HAVE SOMETHING WRONG!!!!!!
YOU have missed something here! YOU are going to have to double back over yourself and check everything again if you expect to find the problem! Did you check the impeller to see if it's not slipping on the shaft? I just bet not. Whoever does? Fact is YOU MISSED SOMETHING!
It's no big deal, but to keep shooting down idea after idea because "YOU KNOW" that's not the problem is pretty ignorant, since you don't know WHAT the problem is!!!!!!!!!!!!!
Not trying to be an *** here, but "I" would damn sure not resort to long term storage simply because I was too hard headed to recheck myself.
