2003 Ford Ranger RPMs getting stuck over 3,000

Two mechanics I trust like you wouldnt understand, a Wyotech graduate, and myself are scratching our heads:
My truck starts up on very high rpms(2,000+) then takes over 15 seconds to idle normal under 1000.
I drive off and make my rpms to rev over 3000 to accelerate and get onto a busy street. If and when I brake, the truck slows down but my rpms stay stuck over 2000. MY brake gets hard to push down. All of a sudden, pms drop to under 1000 and u feel the drop as if u were downshifting. The engine sounds super quiet after this. Never turns off, although it sounds dead from dropping so low. And it accelerates normally.
If I turn the a.C on, the rpms rev from 1000 to 500 as the compressor clicks in and out at an abnormal amount of times. If I turn off the a.C that problem goes away. Again, it accelerates normally and drives smoothly, ven on a highway trip lasting two hours driving no slower than 65- 80 mph. Please help exorcise this truck. Important to remember, every sensor including the idle control sensor has been replaced along with my manifold gasket and a few vacuum line nd the a.C sensors bot h hi and low