Mazda B2600 Pickup-Hesitation problem
 

Hey, Hope you guys can help me out.
I've got a 1987 B2600 4X4 that I've owned for over 10 years. It might get about 500-1000 miles a year put on it.
Recently, it has lost a lot of power and hesitates a LOT.
It started causing problems at about 25-35 MPH. After a can of gas treatment and oil treatment, I got it up to 50MPH.
I also cleaned the carb with spray cleaner and pulled the distributor and cleaned off some white chalk from the tabs inside the cap.
The engine will rev all the way to the redline if you let it.....lots of raw power and will accellerate fairly well up until about 50MPH, when it really starts to bog down, hesitate nad acts like it wants to stall.
when I back off the gas, it runs just fine?
It does have trouble going up hills as well. 4 wheel drive still works.

Where do I start to track down my problem?

The plugs, wires and distributor cap are only about 2 years old.
All of the vacuum lines appear to be attached correctly.

There is a Major exhaust lead from where the header conects up into the air intake(hose is gone)
There is a hole in the pipe that runs next to/below that(a LOT of hot air comes out that hole)
Where the exhaust connects to the pipe behind the resonator?(right below the engine) there is no seal at that point, so a lot of exhaust sneaks out there. (2 pipes feed back up to the engine at that point as well.
The engine used to give a lot of blow-by into the air cleaner, but that has reduced, however, when you remove the oil filler cap with the engine running, it tends to spit oil out at you.

PCV valve seems fine (it rattles)
So, is my problem most likely
EGR/Exhaust related
Timing
Carburetor
other?

The truck seems to have a good amount of torque...as when I put it into 4 wheel drive and pull the emergengy brake, the front wheels will pull the card foward easily.

I'm somewhat handy, but don't even know where to start! (I've never seen so many vacuum hoses and EGR pipes in my life!

HELP!

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