It will stay running in park an neutral but die in gear, it is getting good fuel pressure,I ain't getting no codes. If iac is idle air control yes the old one was used.

How does the old Iac pertain to my issue?

 

If the old IAC worked before, it should work just fine now as well. Yours sounds for all the world like a locked TCC.

 

So where do I go from here if it is a locked up tcc?
Now is that the torque converter control solenoid? Replace that or does that mean the torque converter is bad?

 

Ok so I removed the transmission relay under the hood an the truck will now move an stay running but feel.as if it is slipping I'd imagine it would without the relay but what does this mean what do I have to do next

 

Plug the relay back in. Unplug the 8 pin connector at the transmission. (drivers side, 'bout halfway back) Check the Orange w/black trace wire for continuity to ground. See what ya get.

 

With the key on I would imagine? Or should I have tho motor running

 

Ok so the I pulled the trans relay an truck moved but trans slipped (of course).

I replaced the relay an the truck moves just fine now.

I would imagine that this isn't something to ignore an that the issue will repeat sometime again. I know you said to check the continuity but I couldn't find an 8 pin connector halfway back is it on the trans?

 

Drivers side of the trans. Goes straight down into the top of the valve body.

Have you driven it around a bit?

 

Yes I have drove it around I've put another 50 miles on it since it started working again an it hasn't done it since an has been running fine?

 

You put the relay back in? Or you replaced it with a new one? If it was a bad/stuck relay and you put a new one in, I'd just drive it. If you put the old one back in and it's not stuck, maybe consider replacing it for peace of mind.