in my 04 4.0 gc i just put in a brand new reman motor. wasnt easy but i did it. it is runing great with 1 exception. randomly the engine will loose power verry momentarly like its cutting out only once in a while. it only cuts out for a second. the tach and the speedo bolth start droping untill it catches itself. with an obd2 tool connected, during this cutting out all sensor values on the tool(
verry nice obd2 dataloger) cut to zero. the tps, iat, clt ect. on the scan tool drop to zero. its almost like the key is shut off but its not. any input apreciated.

 

This might be a hard one to find, but it really sounds like you might have a loose connection somewhere, maybe didnt get a connector seated all the way, forgot to attach a ground or loose ground wire. PCM connectors, battery terminals, fuses relays etc...

You might try to wiggle all the harnesses under the hood and see if you can duplicate the concern. It wouldn't be a bad idea to get a can of electrical contact cleaner (auto parts store) and some electrical grease. Unplug connections and spray a little cleaner in them, let it dry and put a small amount of elec grease on terminals and re-connect.

 

ill give everything a good look over and see what happens