96 sierra issues

[onelozu]

Okay so I just pulled the 350 out if my truck for a rebuild and stuck a 305 in for the meantime,gonna be slow on the rebuild so I'd like to drive it for now. I pulled the 305 out of my parts truck that I was driving for about 3 months,motor ran perfect to issues what so ever,so I swapped motor wiring and ecu from the donor truck. I got the truck running but it would spit and sputter bad and had a hesitation,figuring it was water in the gas(which it was) i drained the tank completely dry,then changed the fuel filter,pump,and fuel pump strainer,and put 10 gallons of fresh gas.this cleared the problem a little but it was still bad so figuring the spark plugs probably got wet and ruined I replaced those,and that cleared it up a lot,now it runs almost perfect but only when it's warmed up. The maf,plug wires,cap,rotor,and ignition coil are all off the 350 but less than a year old,I'd say less than 4k miles on it all,Is there any thing I'm missing? I have a check engine light but can't read the codes cause the obd port doesn't work for some reason,it worked when I had the 350 but now it doesn't want to come up. Any ideas?? I could really use the help

 

[1996k1500]

What year are the engines? And it sounds like something isn't connected properly for the OBDII.