My throttle cuts out, sometimes it works and sometimes it wont

[Bulldog88]

So I installed and 04 model motor in my truck, and I have the tac, pedal, and ecm from it, and sometimes the pedal will work and sometimes it won't, for example if I turn the truck on and I rev the motor up it will do it 2 -3 times then the pedal stops working, then if I shut it off and turn it back on it will work again sometimes depending on how long I let it sit. I even went to a salvage yard and got another pedal tac box and harness from a 04 and still nothing, I have not scanned it yet, I'm getting power at the tac box I check that out already so what can it be?