Depends on which 4 speed you're talking about (people have used both the 4L60E and the 4L80E). This is probably my biggest dilemma. I'm ready to start putting stuff together and I
still haven't decided on which engine and transmission I'm going to run. I've been researching this for
months, I already have an LM7/4L60E, but my gut is telling me to pick up a 6.0L/6L80E. I feel like if I swap in the LM7/4L60E I'm going to have regrets. The cost difference between the engine/transmission combo's is only about $1.5k-$2k once I factor in refreshing (not rebuilding) the LM7 and rebuilding the 4L60E (due to their reliability issues, I won't run a used one in my overland rig).
Based on my research (please correct me if I'm wrong guys), the 6L80E/6L90E is much stronger than the 4L60E, has better gearing, and you can find low mileage units for
half the cost of rebuilding the 4L60E. Downsides are that It's also more difficult to program and getting to the computer to send it out for a tune requires removing the oil pan. From what I've seen, it seems like the Gen4/6L80E swap itself (beyond just the cost of the engine/transmission) is more difficult and more expensive. So far I'm leaning toward
this PSI kit for wiring/programming if I go with the Gen4/6L80E.
I really appreciate you taking the time to write this up, it helps. My first option is to put a cam in my LM7 and run it with the 4L60E. My second option is to purchase a low mileage Gen4 6.0L and a 6L80E. After reading this I'm pretty sure the added difficulty and expense of the 6.0L and 6L80E would be worth it for me. I'm hoping to get as much range as possible, and for that I think the 5.3L might be better than a 6.0L (I've heard mixed things), so I'm looking forward to seeing your MPG notes.