Help, 1993 4.3L not feeling very good.

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I have a 1993 GMC 4/4 4.3L TB 5 speed with 220,000 miles onit. After going 2 or 3 miles down the road the truck will want to die out, but if i down shift into 4th gear and put it to the floor it will take off again. I had a scan tool hooked up to it and this is what i saw, LOOP CLOSED, RICH/LEAN switching ok. Even when it's dieing out the scan tool will read RICH and Lean so i'm thinking that it's not a fuel problem. I had 1 code 42. This is what i have done to it so far.
I just replaced the motor with a GMGOODWRENCH reman. But i did notice the old motor also had a dead spot init about 1/2 throttle to, but it started to knock so i pulled it out.
New O2 sensor, TB base gasket, Plugs
I've tried unhooking the EGR valve vac line=same problem
I've checked the timming, set at zero=same problem
New fuel pump assmb=same problem
New fuel filter=same problem
There is no cat on the trk, by the way i just bought this trk a month ago.
What it feels like is the truck is running out of fuel, no poping or jerking just loss of power, even if i try to give it more throttle in over drive nothing changes untill i down shift then it will take off but kinda jerky..?? If theres any thing you would like me to post off the scan tool let me know.
Thanks for your help. Dave