I have a 02 5.3 out of a Yukon that I had swapped in my 02 Jeep Wrangler TJ. Using the transmission and transfer case from the Jeep and my Jeep computer runs my gauges and the 5.3 computer runs the engine.
Ok it starts just fine and will idle just fine but I can on the highway and drive around 20 min. At 65 to 70 with no problem. When I hit the exit ramp and start to slow down going into 3rd and 2nd gear my rpms drop to 0 and it dies. It starts right back up and will sit there and idle waiting on the light to change. Coming off a higher speed in 4th and 5th gear and slowing down for a stop it just dies.
i would appreciate any help you could send my way.

 

Is the 5.3 computer still flashed for an automatic? You need a tune....

 

+1 to G Atsma's comment, a tune is a given.

Did a similar swap, 325 Gen III + NV4500 5 speed into my Scout.

Tune helped a lot, but the tuner commented that if I experienced the engine dying at stop signs, etc, I needed to run a speed sensor.

I have a Dakota Speed, speed sensor in a box that I have purchased, don't have it on the vehicle yet.

Minimally, hopefully this provides another perspective.

 

There's a forum for diagnostics/tuning.

 

just an idea, please check my old thread:

https://ls1tech.com/forums/automatic...l#post19443784

I had same issue, and it was an EGR problem.

 

An EGR valve hanging open will definitely stall an engine.