I have 1998 Mazda B2500 2.4L 4 cylinder manual transmission pickup that has a vacuum leak that I cannot find. The engine has roughly 255,000 miles on it.

Symptoms:
Once the truck start and is warming up, if I rev the engine above 4000 rpm's, after I release the throttle the engine dies. I then start the truck again and it idles very rough. If I let the engine completely warm up, then I won't have this issue. Also, I disconnected all the vacuum hoses from the engine, minus the intake from the air filter, and hooked up a vacuum tester directly to the engine. The needle was vibrating 1-2Hg around the 19Hg mark.

It is not throwing any codes and it is passing SMOG though it is consuming more gas than before.

I have tested all the vacuum hoses coming from the engine and they have suction.

Any ideas?