2000 Explorer 5.0 goes limp just after it starts rolling.

[Elgatoprerunner]

I just finished the v8 swap into my desert truck. The motor runs great when the truck isn't rolling. When I put it in gear at approximately 2-3 mpg the engine goes into limp mode.
Does anyone know why it's doing this?

2000 5.0 from a awd explorer
Dana 20
Wiring harness cut down and simplified.
ECU reprogrammed pats delete, smog delete, custom tune
No vss


Any help is appreciated.

 

[Dono]

Can you pull the engine codes? No one can say much without knowing the codes causing the limp mode.

 

[Elgatoprerunner]

I need my wiring guy to wire me in a obd2 port.
I have no way of reading codes until that happens.

 

[Dono]

Ouch. I really don't know what to say. There are a bunch of threads on what happens with no vss signal, and it looks kind of like it depends what year of pcm you have. Without knowing codes, it's best guess.