truck only running in open loop?

[uncabob]

Did the swap include the ECM?
Bob

[joegreen]

No. Everything stayed just the motor was swapped.

[jim_in_dorris]

There are a couple of possibilities, if it used to run closed loop. First make sure that you are seeing the o2 sensor swing, If it doesn't see an o2, it wont go closed loop. Second, look at the coolant temp, it wont go closed loop until it warms up. also you could be in limp mode.