My S-10 (4.3 liter engine V-6) when it first starts up & try to take off the engine bogs down, won't hardly pull it's self out of it's tracks. After about 2 blocks it runs GEAR! But if I shut it off for just a minute then try & drive it same thing it won't hardly run for about 2 blocks then after that it runs great. I've had it to 2 shops & they've run there diagnostic analyzers (A Snap-on & the other is a Altest? And these mechanic's are really good & both run a auto repair shops. BUT! The analyzers show nothings wrong? So there just guessing to replace the airflow meter or the pressure valve under the manifold? But I ain't got a gold mine in my lower half & know from past experience you just guess at these new cars lol? Any ideals?