Terrible mileage, poor acceleration, hesitation
 

I've got an '89 s10 blazer, 4x4, with the 4.3L. Right now it's getting about 10mpg. It runs well on the highway but accelerates poorly at any speed. When slowing to leave the highway, ie going from 60-70 to 30ish, it bogs down like its flooding then goes back to normal. Occasionally, it will do the same thing while leaving a stop sign. The oil pressure also runs very low at idle, check gauges light comes on.
The vapor canister has been taken out and the lines capped, not sure if this could be creating problems?
I was getting a code 45 (rich exhaust), but after replacing the tps and coolant sensor, though it seems to run the same, I'm getting code 13 and 44 (lean exhaust indicators).

Is it TBI? do a leak down test. Can find instructions on how to do that by searching the site.